Synchronous switching apparatus for use with a multiple phase power system

ABSTRACT

A synchronous switching apparatus for detecting a source voltage of each phase to close each phase at an electrical phase angle predetermined for each phase, including switching devices  1   a-   1   c  provided one for each phase for opening and closing an impedance load, switching devices  2   a-   2   c  for closing and opening the switching devices  1   a-   1   c  for each phase, measuring transformers  5   a-   5   c  for measuring source voltages of the respective phases and phase-to-phase voltages, and phase control devices  42  each for issuing a command for energizing the impedance load at an electrical phase angle in a range predetermined for each phase, when detecting a zero point of a source voltage of each phase or a zero point of each phase-to-phase voltage.

TECHNICAL FIELD

The present invention relates to a synchronous switching apparatus foruse with a multiple phase power system that controls the opening andclosing timing of a power switch to suppress the occurrence of excitinginrush currents and surge voltages, which are hard on system equipmentsuch as transformer, shunt reactor, power-transmission lines andcapacitor banks.

BACKGROUND ART

In the closing and opening of a power switch, many methods forsuppressing transient phenomena that are hard on system equipment havebeen proposed. For example, “Development of a gas-blast circuit breakerfor 1000 kV GIS,” included in The 1994 Electric Society NationalSymposium Proceedings, pages 1453-1455, describes power switchingequipment (circuit breaker) in which as means for suppressing surgevoltages generated in system equipment such as transformer and shuntreactor, a resistor on the order of 500 to 1000 ohms is inserted beforeclosing the switching equipment. FIG. 7 shows the case in which a shuntreactor is energized by using this resistor insertion technique. In FIG.7, (1 a), (1 b), and (1 c) are switching devices provided for R, S and Tphases, respectively; (2 a), (2 b), and (2 c) are switching devices forclosing or opening the switching device for the R, S and T phases,respectively; (8 a), (8 b) and (8 c) are switches for insertingresistors (7 a), (7 b) and (7 c), respectively, which are connected inparallel with the switching devices for the R, S and T phases,respectively; (9 a), (9 b) and (9 c) are reactor banks to be inserted;(5 a), (5 b) and (5 c) are measuring transformers used for measuring thesource voltage of each of the R, S and T phases, respectively; and (4)is a control device for issuing closing commands to each switchingdevice (1) and each switch (8).

When the switching devices of the conventional resistor insertiontechnique configured in this way are used to energize the reactor banks(9), first, the control device (4) issues a closing command to each ofthe switches (8 a), (8 b) and (8 c), and source voltage are applied tothe reactor banks (9) through the resistors (7 a), (7 b) and (7 c). Thecurrents caused by transient surge voltages upon inserting the resistorsare rapidly damped by the resistors. Therefore, a voltage of smallamplitude and having the same frequency as the source voltage is appliedto the reactor banks (9). Subsequently, the control device(4) issuesclosing commands to each of switching mechanism (2 a), (2 b) and (2 c).Then, when the switching equipment is closed, transient phenomena can besuppressed and exciting inrush currents flowing into the reactor banks(9) can be also suppressed, because a voltage of the same phase as thatof the source voltage has already been applied to the reactor banks (9)through the resistors.

However, this method has problems in that the switching equipment is notonly comparatively expensive but also large because the method requiresthat the resistor elements and the switches for inserting the resistorshaving the capacity needed for each piece of equipment, must be providedinside the switching equipment.

Further, in the case of energizing transmission lines, it is impossibleto suppress surges with the inserting resisters if the lines are long.Therefore, when energizing system equipment such as transformer andshunt reactor, in principle, the occurrence of transient exciting inrushcurrents and surge voltages can be suppressed by energizing at the peakvalue (an electrical phase angle of 90 degrees) of the source voltage.This is discussed by CIGRE et al. and disclosed in “ControlledSwitching”, ELECTRA. NO. 164, (1995) and ELECTRA. NO. 165, (1995).

FIG. 8 shows an operating sequence when a transformer is energized usingthis synchronous switching apparatus. In FIG. 8, (1 a), (1 b) and (1 b)are switching devices provided for the R, S and T phases, respectively;(2 a), (2 b) and (2 c) are switching mechanisms for closing or openingthe switching devices for the R, S and T phases, respectively; (3) is atransformer to be energized; (5 a), (5 b) and (5 c) are measuringtransformers used for measuring the respective source voltage of the R,S and T phases; (40) is a phase control device for issuing closingcommands to the switch mechanism (2) of each switching device (1).

When the transformer (3) is energized using the synchronous switchingapparatus configured in this way, first the transformers (5 a), (5 b)and (5 c) used for measuring the respective source voltage of the R. Sand T phases detect the zero points of the respective source voltage ofthe R. S and T phases. The phase control device(40) estimates “apole-closing time Tc” which is the time until an electrical phase angleof a certain ideal angular phase is reached based on the operating timeof the switching mechanism as determined from the temperature, operatingvoltages and past operating history as shown in FIG. 9, and then adjusts“the delay time Td” for outputting a closing signal such that closingmay be established at a closing time Ta corresponding to the targetelectrical phase angle of each of the R, S and T phases, and provides aclosing command to each of the switching mechanism (2 a), (2 b) and (2c). By closing the switching equipment for the transformer (3) at thepredetermined closing time according to this command, in principle,transient phenomena can be suppressed.

Further, “Development of a gas-blast circuit breaker for 1000 kV GIS”,included in The 1994 Electric Society National Symposium Proceedings,pp. 1453-1455, illustrates a power switch (circuit breaker)” thatsuppresses surge voltages generated in system equipment, such aspower-transmission lines and capacitor banks, by inserting a resistor onthe order of 500 to 1000 ohms before closing the switching equipment, asshown in FIG. 10.

FIG. 10 shows the case of energizing capacitor banks using the switchingequipment according to this resistor insertion technique. In thisfigure, similar reference characters are used to refer to portions thatare identical or correspond to those in FIG. 7. In FIG. 10, (9 a 1), (9b 1) and (9 c 1) show capacitor banks to be energized.

By using the conventional switching devices according to the resistorinsertion technique configured as above, when the capacitor banks (9 a1), (9 b 1) and (9 c 1) are energized, first the control device (4)issues a closing command to each of the switches (8 a), (8 b) and (8 c),and source voltage are applied to the capacitor banks (9 a 1), (9 b 1)and (9 c 1) through the resistors (7 a), (7 b) and (7 c).

A current occurring due to a transient surge voltage upon inserting theresistor(s) is rapidly damped by the resistor(s). Therefore, a voltagehaving a small amplitude and with the same frequency as the sourcevoltage is applied to the capacitor banks (9 a 1), (9 b 1) and (9 c 1).Subsequently, the control device (4) issues a closing command to each ofthe switch mechanism (2 a),. (2 b) and (2 c). Then, when the switchingequipment is closed, transient phenomena can be suppressed and excitinginrush currents flowing into the capacitor banks (9 a 1), (9 b 1) and (9c 1) can also be suppressed because a voltage which is in phase with thesource voltage has already been applied to the capacitor banks (9 a 1),(9 b 1) and (9 c 1) through the resistors.

However, this method has problems in that the switching equipment is notonly comparatively expensive but also has a large size because thismethod requires that the resistor elements and switches for insertingthe resistors having the capacity needed for each piece of equipment,must be provided inside the switching equipment. Further, in the case ofenergizing transmission lines, it is impossible to suppress surges byinserting resisters for long transmission lines.

Therefore, when energizing system equipment such as transmission linesand capacitor banks, the occurrence of transient exciting inrushcurrents and surge voltages can be, in principle, suppressed byenergizing at the zero point(0) of the electrical phase angle of thesource voltage. This is discussed by CIGRE et al. and disclosed in“Controlled Switching”, ELECTRA. NO. 164, (1995) and ELECTRA. NO. 165,(1995).

FIG. 11 shows an operating sequence when energizing a transformer usingthis synchronous switching equipment. In FIG. 11, (1 a), (1 b) and (1 c)are switching devices provided for the R, S and T phases, respectively;(2 a), (2 b) and (2 c) are switching devices for closing or opening theswitching devices for the R, S and T phases, respectively; (3 a), (3 b)and (3 c) are transmission lines to be energized, respectively; (5 a),(5 b) and (5 c) transformers are used for measuring the source voltageof the R, S and T phases, respectively; a phase control device (40)issues a closing command to the switch mechanism (2) for each switchingdevice (1).

In the synchronous switching apparatus structured as above, whenenergizing each of the transmission lines (3 a), (3 b) and (3 c), first,the transformers (5 a), (5 b) and (5 c) used for measuring the sourcevoltage of each of the R, S and T phases detect the zero point of thesource voltage of each of the R, S and T phases, respectively. The phasecontrol device (40) estimates “a pole-closing time Tc” which is the timeuntil an electrical phase angle of a certain ideal angular phase isreached based on the operating time of the switching mechanism asdetermined from the temperature, operating voltages and past operatinghistory as shown in FIG. 12, and adjusts “the delay time Td” foroutputting a closing signal such that closing may be established at aclosing time Ta corresponding to the target electrical phase angle ofeach R, S and T phase to provide a closing command to each of theswitching mechanisms (2 a), (2 b), (2 c). By closing the switchingequipment for the transmission lines (3 a), (3 b) and (3 c) at thepredetermined closing time according to this command, in principle,transient phenomena can be suppressed.

However, because the time required for closing switching equipmentinevitably varies due to variations in mechanical characteristics andthe occurrence of discharge, ideal closing is not always realized.

The present invention has been made to overcome the above-describedproblems, and an object of the invention is to provide feasible closingtiming to the switching equipment for each phase.

SUMMARY OF INVENTION

The present invention overcomes the above described problems andachieves the above discussed objectives by providing a synchronousswitching apparatus for use with a multiple phase power system having aplurality of phases and for detecting a source voltage of each phase andenergizing each phase at an electrical phase angle predetermined foreach phase. The synchronous switching apparatus includes a plurality ofswitching devices, one switching device being provided for each phaseand opening and closing an impedance load. The synchronous switchingapparatus further includes a plurality of switching mechanisms, whichclose and open the switching devices, and a plurality of voltagemeasuring transformers, which measure source voltages of the phases. Inaddition, the synchronous switching apparatus includes a plurality ofphase-to-phase voltage measuring transformers, which measure respectivephase-to-phase voltages, and a plurality of phase control devices. Onephase control device is provided for each phase and issues a command toenergize the impedance load with a source voltage at an electrical phaseangle in a range predetermined for the phase, in response to detectionof a zero point of a source voltage of the phase by the voltagemeasuring transformer or in response to detection of a zero point of thephase-to-phase voltage by the phase-to-phase voltage measuringtransformer.

A second embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of a single-phase core transformer orshunt reactor with a neutral point grounded. For this embodiment, aswell as for the third through nineteenth embodiments, the plurality ofphases includes a first (R), a second (S), and a third (T) phase, andthe plurality of voltage measuring transformers includes a first, asecond, and a third voltage measuring transformer, which measure sourcevoltages of the first, second, and third phases, respectively. Inaddition, the predetermined electrical phase angles of each of thefirst, second, and third phases are within a range of 90 degrees(voltage peak value of the R, S, and T phases)±90 degrees.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first (R) phase at the predeterminedelectrical phase angle of the first phase in response to detection of azero point of a first (R) phase source voltage by the first voltagemeasuring transformer, a second command for energizing the third (T)phase at the predetermined electrical phase angle of the third phase inresponse to detection of a zero point of a third (T) phase sourcevoltage by the third voltage measuring transformer at a time around ⅓ ofa cycle after an energizing time of the first (R) phase, and a thirdcommand for energizing the second (S) phase at the predeterminedelectrical phase angle of the second phase in response to detection of azero point of a second (S) phase source voltage by the second voltagemeasuring transformer at a time around ⅓ of a cycle after an energizingtime of the third (T) phase.

A third embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of a single-phase core transformer orshunt reactor with a neutral point grounded. The plurality ofphase-to-phase voltage measuring transformers comprises afirst-to-second (R-to-S), a second-to-third (S-to-T), and athird-to-first (T-to-R) phase voltage measuring transformer, whichmeasure a first-to-second, a second-to-third, and a third-to-first phasevoltage, respectively. The predetermined electrical phase angles of eachof the first-to-second phase voltage, the second-to-third phase voltage,and the third-to-first phase voltage are within a range of 60 degrees±20degrees.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first (R) phase at the predeterminedelectrical phase angle of the first-to-second (R-to-S) phase voltage inresponse to detection of a zero point of the first-to-second phasevoltage by the first-to-second phase voltage measuring transformer, asecond command for energizing the third (T) phase at the predeterminedelectrical phase angle of the third-to-first (T-to-R) phase voltage inresponse to detection of a zero point of the third-to-first (T-to-R)phase voltage by the third-to-first phase voltage measuring transformerat a time around ⅓ of a cycle after an energizing time of the firstphase, and a third command for energizing the second (S) phase at thepredetermined electrical phase angle of the second-to-third (S-to-T)phase voltage in response to detection of a zero point of thesecond-to-third (S-to-T) phase voltage by the second-to-third phasevoltage measuring transformer at a time around ⅓ of a cycle after anenergizing time of the third (T) phase.

A fourth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of a three-phase core transformer or shuntreactor having star-connected windings with a neutral point grounded.The plurality of voltage measuring transformers includes a first and athird voltage measuring transformer, which measure source voltages ofthe first and third phases, respectively. The predetermined electricalphase angle of the first phase is within a range of 90 degrees (voltagepeak value of the R phase) ±20 degrees, and the electrical phase angleof the third phase is within a range of 60 degrees ±20 degrees.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first (R) phase at the predeterminedelectrical phase angle of the first phase in response to detection of azero point of a first (R) phase source voltage by the first voltagemeasuring transformer, a second command for energizing the third (T)phase at the predetermined electrical phase angle of the third phase inresponse to detection of a zero point of a third (T) phase sourcevoltage by the third voltage measuring transformer at a time around ¼ ofa cycle after an energizing time of the first (R) phase, and a thirdcommand for energizing the second (S) phase at any time after theenergizing of the third (T) phase.

A fifth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of a single-phase core transformer orshunt reactor with a neutral point grounded. The plurality of voltagemeasuring transformers includes a first and a second voltage measuringtransformer, which measure source voltages of the first and secondphases, respectively.

The predetermined electrical phase angle of the first phase is within arange of 90 degrees (voltage peak value of the R phase) ±20 degrees, andthe predetermined electrical phase angle of the second phase is within arange of −30 degrees ±20 degrees.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first (R) phase at the predeterminedelectrical phase angle of the first phase in response to detection of azero point of the first (R) phase source voltage by the first voltagemeasuring transformer, a second command for energizing a second (S)phase at the predetermined electrical phase angle of the second phase inresponse to detection of a zero point of a second (S) phase sourcevoltage by the second voltage measuring transformer at a time around ¼of a cycle after an energizing time of the first (R) phase, and a thirdcommand for energizing the third (T) phase at any time after theenergizing of the second phase.

A sixth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of a single-phase core transformer orshunt reactor with a neutral point grounded. The plurality ofphase-to-phase voltage measuring transformers includes a first-to-second(R-to-S) and a third-to-first (T-to-R) phase voltage measuringtransformer, which measure a first-to-second and a third-to-first phasevoltage, respectively.

The predetermined electrical phase angle of the first-to-second phasevoltage is within a range of 60 degrees ±20 degrees, and thepredetermined electrical phase angle of the third-to-first phase voltageis within a range of 30 degrees ±20 degrees.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first (R) phase at the predeterminedelectrical phase angle of the first-to-second (R-to-S) phase voltage inresponse to detection of a zero point of the first-to-second phasevoltage by the first-to-second phase voltage measuring transformer, athird command for energizing the third (T) phase at the predeterminedelectrical phase angle of the third-to-first (T-to-R) phase voltage inresponse to detection of a zero point of a third-to-first (T-to-R) phasevoltage by the third-to-first phase voltage measuring transformer at atime around ⅓ of a cycle after an energizing time of the first (R)phase, and a second command for energizing the second (S) phase at anytime after the energizing of the third (T) phase.

A seventh embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of a three-phase core transformer or shuntreactor having star-connected windings with a neutral point grounded.The plurality of phase-to-phase voltage measuring transformers comprisesa first-to-second (R-to-S), and a second-to-third (S-to-T), whichmeasure a first-to-second and a second-to-third phase voltage,respectively.

The predetermined electrical phase angles of the first-to-second and thesecond-to-third phase voltage are within a range of 60 degrees ±20degrees and −60 degrees ±20 degrees, respectively.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first (R) phase at the predeterminedelectrical phase angle of the first-to-second (R-to-S) phase voltage inresponse to detection of a zero point of the first-to-second (R-to-S)phase voltage by the first-to-second phase voltage measuringtransformer, a second command for energizing the second (T) phase at thepredetermined electrical phase angle of the second-to-third (S-to-T)phase voltage in response to detection of a zero point of thesecond-to-third (S-to-T) phase voltage by the second-to-third phasevoltage measuring transformer at a time around ⅓ of a cycle after anenergizing time of the first phase (R phase), and a third command forenergizing the third (T) phase at any time after the energizing of thesecond (S) phase.

An eighth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of a three-phase core transformer or shuntreactor having star-connected windings with a neutral point ungrounded,or a delta connection transformer or shunt reactor. The plurality ofvoltage measuring transformers includes a first and a third voltagemeasuring transformer, which measure source voltages of the first andthird phases, respectively. The predetermined electrical phase angles ofthe first and third phases are within a range of 120 degrees ±20 degreesand 90 degrees ±20 degrees, respectively.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the second (S) phase at any time, a secondcommand for energizing the first (R) phase at the predeterminedelectrical phase angle of the first (R) phase in response to detectionof a zero point of a first (R) source voltage by the first voltagemeasuring transformer after the energizing of the second (S) phase, anda third command for energizing the third (T) phase at the predeterminedelectrical phase angle of the third (T) phase in response to detectionof a zero point of a third (T) phase source voltage by the third voltagemeasuring transformer at a time around ⅓ of a cycle after an energizingtime of the first (R) phase.

A ninth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of a three-phase core transformer or shuntreactor having star-connected windings with a neutral point ungrounded,or a single-phase core and three-phase core delta connection transformeror shunt reactor. The plurality of voltage measuring transformersincludes a second and a third voltage measuring transformer, measuringsource voltages of the second and third phases, respectively. Thepredetermined electrical phase angles of the second and third phases arewithin a range of −120 degrees ±20 degrees and 90 degrees ±20 degrees,respectively.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first (R) phase at any time, a second commandfor energizing the second (S) phase at the predetermined electricalphase angle of the second (S) phase in response to detection of a zeropoint of a second (S) phase source voltage by the second voltagemeasuring transformer after the energizing of the first (R) phase, and athird command for energizing the third (T) phase at the predeterminedelectrical phase angle of the third (T) phase in response to detectionof a zero point of a third (T) phase source voltage at a time around ⅓of a cycle after an energizing time of the second (S) phase.

A tenth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of a three-phase core transformer or shuntreactor having star-connected windings with a neutral point ungrounded,or a single-phase core and three-phase core delta connection transformeror shunt reactor. The plurality of phase-to-phase voltage measuringtransformers includes a first-to-second (R-to-S phase) and athird-to-first (T-to-R) phase voltage measuring transformer, whichmeasure a first-to-second and a third-to-first phase voltage,respectively. The predetermined electrical phase angles of thefirst-to-second and third-to-first phase voltages are within a range of90 degrees ±20 degrees and 60 degrees ±20 degrees, respectively.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the second (S) phase at any time, a secondcommand for energizing the first (R) phase at the predeterminedelectrical phase angle of a first-to-second (R-to-S) phase voltage inresponse to detection of a zero point of a first-to-second (R-to-S)phase voltage by the first-to-second phase voltage measuring transformerafter an energizing time of the second (S) phase, and a third commandfor energizing the third (T) phase at the predetermined electrical phaseangle of a third-to-first (T-to-R) phase voltage in response todetection of a zero point of a third-to-first (T-to-R) phase voltage bythe third-to-first phase voltage measuring transformer at a time around⅓ of a cycle after an energizing time of the first (R) phase.

An eleventh embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of a three-phase core transformer or shuntreactor having star-connected windings with a neutral point ungrounded,or a single-phase core and three-phase core delta connection transformeror shunt reactor. The plurality of phase-to-phase voltage measuringtransformers includes a second-to-third (S-to-T) and a third-to-first(T-to-R) phase voltage measuring transformer, which measure asecond-to-third and a third-to-first phase voltage, respectively. Thepredetermined electrical phase angles of the second-to-third and thethird-to-first phase voltages are within a range of −150 degrees ±20degrees and 60 degrees ±20 degrees, respectively.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first (R) phase at any time, a second commandfor energizing the second (S) phase at the predetermined electricalphase angle of a second-to-third (S-to-T) phase voltage in response todetection of a zero point of a second-to-third (S-to-T) phase voltage bythe second-to-third phase voltage measuring transformer after anenergizing of the first (R) phase, and a third command for energizingthe third (T) phase at the predetermined electrical phase angle of athird-to-first (T-to-R) phase voltage in response to detection of a zeropoint of a third-to-first (T-to-R) phase voltage by the third-to-firstphase voltage measuring transformer at a time around ⅓ of a cycle afteran energizing time of the second (S) phase.

A twelfth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the second embodiment, but whichis for use with an impedance load in the form of capacitor banks with aneutral point grounded or transmission lines without an electric charge.In addition, the predetermined electrical phase angles of each of thefirst, second, and third phases are within a range of 0 degrees (zerovoltage points of the R, S, and T phases) ±20 degrees.

A thirteenth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the third embodiment, but whichis for use with an impedance load in the form of capacitor banks with aneutral point grounded or transmission lines without an electricalcharge. In addition, the predetermined electrical phase angles of eachof the first-to-second phase voltage, the second-to-third phase voltage,and the third-to-first phase voltage are within a range of −30 degrees±20 degrees.

A fourteenth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of capacitor banks with a neutral pointungrounded. The plurality of voltage measuring transformers includes asecond and a third voltage measuring transformer, which measure sourcevoltages of the second and third phases, respectively. The predeterminedelectrical phase angles of the second and third phases are within arange of 0 degrees ±20 degrees and 30 degrees ±20 degrees, respectively.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first (R) phase at any time, a second commandfor energizing the third (T) phase at the predetermined electrical phaseangle of the third (T) phase in response to detection of a zero point ofthe third (T) phase source voltage by the third voltage measuringtransformer after an energizing of the first (R) phase, and a thirdcommand for energizing the second (S) phase at the predeterminedelectrical phase angle of the second (S) phase in response to detectionof a zero point of a second (S) phase source voltage by the secondvoltage measuring transformer at a time around ¼ of a cycle after anenergizing time of the third (T) phase.

A fifteenth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the eighth embodiment, but whichis for use with an impedance load in the form of capacitor banks with aneutral point ungrounded. In addition, the predetermined electricalphase angle of the first phase is within a range of 30 degrees ±20degrees, and the predetermined electrical phase angle of the third phaseis within a range of 0 degrees ±20 degrees. Also, the respective phasecontrol device issues the third command for energizing the third (T)phase at the predetermined electrical phase angle of the third (T) phasein response to detection of a zero point of a third (T) phase sourcevoltage by the third voltage measuring transformer at a time around ¼ ofa cycle after a energizing time of the first (R) phase.

A sixteenth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of capacitor banks with a neutral pointungrounded. The plurality of voltage measuring transformers includes afirst and a third voltage measuring transformer, which measure sourcevoltages of the first and third phases, respectively. The predeterminedelectrical phase angles of the first and third phases are within a rangeof 30 degrees ±20 degrees and 0 degrees ±20 degrees, respectively.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the second (S) phase at any time, a secondcommand for energizing the first (R) phase at the predeterminedelectrical phase angle of the first (R) phase in response to detectionof a zero point of a first (R) phase source voltage by the first voltagemeasuring transformer after the energizing of the second (S) phase, anda third command for energizing the third (T) phase at the predeterminedelectrical phase angle of the third (T) phase in response to detectionof a zero point of a third (T) phase source voltage by the third voltagemeasuring transformer at a time around ¼ of a cycle after a energizingtime of the first (R) phase.

A seventeenth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of capacitor banks with a neutral pointungrounded. The plurality of phase-to-phase voltage measuringtransformers includes a second-to-third (S-to-T) and a third-to-first(T-to-R) phase voltage measuring transformer, which measure asecond-to-third and a third-to-first phase voltage, respectively. Thepredetermined electrical phase angles of the second-to-third and thethird-to-first phase voltages are within a range of −30 degrees ±20degrees and 0 degrees ±20 degrees, respectively.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first (R) phase at any time, a second commandfor energizing the third (T) phase at the predetermined electrical phaseangle of a third-to-first (T-to-R) phase voltage in response todetection of a zero point of a third-to-first (T-to-R) phase voltage bythe third-to-first phase voltage measuring transformer after theenergizing of a first (R) phase, and a third command for energizing thesecond (S) phase at the predetermined electrical phase angle of asecond-to-third (S-to-T) phase voltage in response to detection of azero point of a second-to-third (S-to-T) phase voltage by thesecond-to-third phase voltage measuring transformer at a time around ¼of a cycle after an energizing time of the third (T) phase.

An eighteenth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the tenth embodiment, but whichis for use with an impedance load in the form of capacitor banks with aneutral point ungrounded. In addition, the predetermined electricalphase angle of the first-to-second phase voltage is within a range of 0degrees ±20 degrees, and the predetermined electrical phase angle of thethird-to-first phase voltage is within a range of −30 degrees ±20degrees. Also, the respective phase control device issues the thirdcommand for energizing the third (T) phase at the predeterminedelectrical phase angle of the third-to-first (T-to-R) phase voltage inresponse to detection of a zero point of a third-to-first (T-to-R) phasevoltage by the third-to-first phase voltage measuring transformer at atime around ¼ of a cycle after a energizing time of the first (R) phase.

A nineteenth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment for use withan impedance load in the form of capacitor banks with a neutral pointungrounded. The plurality of phase-to-phase voltage measuringtransformers comprises a first-to-second (R-to-S) and a second-to-third(S-to-T) phase voltage measuring transformer, which measure afirst-to-second and a second-to-third phase voltage, respectively. Thepredetermined electrical phase angles of the first-to-second and thesecond-to-third phase voltages are within a range of −30 degrees ±20degrees and 0 degrees ±20 degrees, respectively.

The impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the third (T) phase, a second command forenergizing the second (S) phase at the predetermined electrical phaseangle of a second-to-third (S-to-T) phase voltage in response todetection of a zero point of a second-to-third (S-to-T) phase voltage bythe second-to-third phase voltage measuring transformer after theenergizing of the third (T) phase, and a third command for energizingthe first (R) phase at the predetermined electrical phase angle of afirst-to-second (R-to-S) phase voltage in response to detection of azero point of a first-to-second (R-to-S) phase voltage by thefirst-to-second phase voltage measuring transformer at a time around ¼of a cycle after an energizing time of the second (S) phase.

A twentieth embodiment of the present invention provides a synchronousswitching apparatus similar to that of the first embodiment, but furtherincludes surge absorbers, which are provided between respective phasesand ground, for respectively suppressing surge voltages of respectivephases. In addition, surge absorbers are provided between respectivephases for suppressing phase-to-phase surge voltages.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of a synchronous switching apparatus accordingto an embodiment of the invention;

FIG. 2 is a block diagram of a synchronous switching apparatus accordingto another embodiment of the invention;

FIG. 3 is a view for illustrating the operating sequence of thesynchronous switching apparatus of the invention;

FIG. 4 is a view for illustrating the optimum closing timing andmagnetic flux variation for a star connection transformer, or shuntreactor, with a neutral point grounded;

FIG. 5 is a view for illustrating the optimum energizing timing and themagnetic flux variation of a delta connection transformer, or a starconnection transformer of a shunt reactor, or a shunt reactor;

FIG. 6 is a view for illustrating the optimum energizing timing andmagnetic flux variation for ungrounded capacitor banks or transmissionlines;

FIG. 7 is a block diagram of a conventional synchronous switchingapparatus using the resistor insertion method;

FIG. 8 is a block diagram of a conventional synchronous switchingapparatus;

FIG. 9 is a view for illustrating the operating sequence of theconventional synchronous switching apparatus;

FIG. 10 is a block diagram of a conventional switching device using theresistor insertion method;

FIG. 11 is a block diagram of a conventional synchronous switchingapparatus; and

FIG. 12 is a view for illustrating the operating sequence of theconventional synchronous switching apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

FIGS. 1 to 3 illustrate a synchronous switching apparatus of the presentinvention and its operating sequences. In FIG. 1, (1 a), (1 b) and (1 c)are synchronous switching devices provided for R, S and T phases,respectively; (2 a), (2 b) and (2 c) are switching mechanisms forclosing and opening the switching devices for R, S and T phases,respectively; (5 a), (5 b) and (5 c) are measuring transformers (voltagemeasuring transformers) used for measuring the source voltage of the R,S and T phases, respectively; (5 d), (5 e) and (5 f) are measuringtransformers (phase-to-phase voltage measuring transformers) used formeasuring R-to-S, S-to-T and T-to-R phase voltage, respectively; (42) isa phase control device for detecting the zero points of the sourcevoltage of the R, S and T phases as well as the zero points of theR-to-S, S-to-T and T-to-R phase voltage, and for issuing a closingcommand to the switch mechanisms (2) of the switching device (1) throughsignal transmission cable (6); (15 a), (15 b) and (15 c) are surgeabsorbers provided between each of buses (10 a), (10 b) and (10 c),respectively, of the R, S and T phases and ground for suppressingsurges, respectively; (16 a), (16 b) and (16 c) are surge absorbers forsuppressing R-to-S, S-to-T and T-to-R phase surges, respectively.

When system equipment is energized using the synchronous switchingapparatus configured in this way, first, the transformer (5 a), (5 b)and (5 c) for detecting the source voltage of R, S and T phases,respectively, detects the zero points of the source voltage of R, S andT phases, respectively. At the same time, the measuring transformers (5d), (5 e) and (5 f) for measuring R-to-S, S-to-T and T-to-R phasevoltage respectively, detect the zero voltage points of the R-to-S,S-to-T and T-to-R phase voltage respectively. The phase control device42 estimates “a pole-closing time Td” which is the time until anelectrical phase angle of a certain ideal angular phase is reached basedon the operating time as determined from the temperature, operatingvoltages and past operating history adjusts “the delay time Td” foroutputting a closing signal such that closing may be established at aclosing time Ta corresponding to the target electrical phase angle ofeach R, S and T phase voltage, and outputs the closing command.

Alternatively, as shown in the operating sequence of FIG. 3, the phasecontrol device 42 provides closing commands to the switching mechanism(2 a), (2 b) and (2 c) such that closing may be established at theclosing time Ta corresponding to the target electrical-phase-angle ofeach R-to-S, S-to-T and T-to-R phase voltage. Accordingly, when eachphase is energized at the predetermined energizing time, switchingequipment is closed for the transformer (3), so that transient phenomenacan be suppressed. Ideal energizing timing for system equipment such astransformer and shunt reactor is at the peak voltages or zero voltage ofeach phase-to-phase voltage, but not at an intermediate electrical phaseangle of the source voltage of each of the phases. Therefore, moreaccurate closing can be realized by detecting not only the zero voltagepoint of the source voltage of each of the R, S and T phases but alsothe zero voltage point of each of the R-to-S, S-to-T and T-to-R phasevoltage to determine the closing time.

Therefore, when transient phenomena are caused by the operation of otherswitching equipment, a detected zero point of each phase voltage or eachphase-to-phase voltage may deriate. Therefore, surge absorbers (15)provided between the bus lines of the R, S and T phases and ground forsuppressing over voltages and the surge absorbers (16) for suppressingR-to-S, S-to-T and T-to-R phase over-voltage suppress transientphenomena so as to minimize voltage disturbances in each of the R, S,and T phase voltage and in each of the R-to-S, S-to-T and T-to-R phasevoltage. This reduces errors in zero point detection to a minimum. Also,because the closing time of switching equipment inevitably varies due tothe mechanical characteristics of the switching equipment and theoccurrence of discharge, ideal closing is not always realized.

These variations in closing time are on the order of ±0.5 ms inswitching devices with high closing speed, and on the order of ±1.0 msin switching devices with low closing speed. The closing time variationsof ±0.5 ms and ±1.0 ms correspond to ±10 degrees and ±20 degrees incommercial frequencies, respectively. Actually, when the real energizingtiming for system equipment such as transformer and shunt reactordeviates from an ideal closing phase angle by the order of ±110 degrees(about ±0.5 ms from the ideal closing time), the surge voltage andexciting inrush current may rise up to about the surge level which canbe suppressed by the switching device of the resistor insertion systemand this level may be practically used.

Therefore, the invention can provide a switching apparatus whereinvariations in closing time can be controlled to less than 10 degrees(less than ±0.5 ms from a predetermined closing time). When theinvention is applied to a switching apparatus with low closing speed,the real closing can deviate from the ideal closing phase angle by about±20 degrees (about ±1.0 ms from the ideal closing time). Then, the surgevoltage or exciting inrush current generated may be, at maximum, half ofthe surge level caused by the switching devices in which the closingphases are not controlled.

Embodiment 2

More specifically, in the method for detecting each phase voltageaccording to a second embodiment of the present invention, in the casewhere a single-phase core transformer or shunt reactor is energized witha source voltage, as shown in FIG. 4, first, when the voltage measuringtransformer (5 a) detects the zero voltage point of a first phases (Rphase) source voltage, the phase control device 42 operates theswitching mechanisms 2 a to close the switching device 1 a, so that thefirst phase (R phase) is energized at an electrical phase angle of thefirst phase (R phase) within the 70-to-110 degree range, preferablywithin the 80-to-100 degree range. At this timing, the exciting inrushcurrent of the first phase (R phase) can be suppressed because themagnetic flux generated in R phase is steady and hence transientphenomena can not occur. Then, when the voltage measuring transformer 5c detects the zero voltage point of a third phase (T phase) sourcevoltage at a time ⅓ of a cycle after an energizing time of the firstphase (R phase), the phase control device 42 operates the switchingmechanisms 2 c to close the switching device 1 c, and then the thirdphase (T phase) is energized at an electrical phase angle of the thirdphase (T phase) within the 70-to-110 degree range, preferably within the80-to-100 degree range.

At this timing, the exciting inrush current of the third phase (T phase)can be suppressed because the magnetic flux generated in T phase is in asteady state and hence transient phenomena can not occur. Finally, whenthe voltage measuring transformer 5 b detects the zero voltage point ofa second phase (S phase) source voltage at a time ⅓ of a cycle after anenergizing time of the third phase (T phase), the phase control device42 operates the switching mechanisms 2 b to close the switching device 1b, so that the second phase (T phase) is energized at an electricalphase angle of the second phase (S phase) within the 70-to-110 degreerange, preferably within the 80-to-100 degree range. At this timing, theexciting inrush current of the third phase (T phase) can be suppressed,because the magnetic fluxes generated in S phase are in a steady stateand so transient phenomena can not occur.

In the following embodiments, in the energizing operations of the firstphase (R) to the third phase (T), the measuring transformer 5 a, 5 b,and 5 c, phase control device 42, switching devices 2 a, 2 b, and 2 c,and switching devices 1 a, 1 b, and 1 c operate in the same manner as inembodiment 2.

Embodiment 3

With the synchronous switching apparatus of this embodiment according toa third embodiment of the present invention, similarly, in the methodfor detecting phase-to-phase voltage, when a single-phase coretransformer or shunt reactor is energized with a source voltage, first,the zero point of a first-to-second phase (R-to-S phase) voltage isdetected, so that the first phase (R phase) is energized at anelectrical phase angle of the first-to-second phase (R-to-S phase)voltage within the 40-to-80 degree range, preferably within the 50-to-70degree range. Thereby, transient phenomena can be suppressed and theexciting inrush current of the first phase (R phase) can also besuppressed.

Next, the zero point of the third-to-first phase (T-to-R phase) voltageis detected at a time ⅓ of a cycle after an energizing time of the firstphase (R phase), and the third phase (T phase) is energized at anelectrical phase angle of the third-to-first phase (T-to-R phase)voltage within the 40-to-80 degree range, preferably within the 50-to-70degree range. Finally, the zero point of the second-to-third phase(S-to-T phase) voltages is detected at a time ⅓ of a cycle after anenergizing time of the third phase (T phase), and the second phase (Sphase) is energized at an electrical phase angle of the second-to-thirdphase (S-to-T phase) voltage within the 40-to-80 degree range,preferably within the 50-to-70 degree range.

Embodiment 4

Using the synchronous switching apparatus of this embodiment accordingto a fourth embodiment of the present invention, by the method ofdetecting each phase voltage, where a three phase core transformer orshunt reactor having star connected windings with a neutral pointgrounded is energized with a source voltage, first, the zero point ofthe first phase (R phase) source voltage is detected, so that the firstphase (R phase) is energized at an electrical phase angle of the firstphase (R phase) within the 70-to-110 degree range, preferably within the80-to-100 degree range.

Accordingly, the transient phenomena can be suppressed and the excitinginrush current of the first (R phase) can also be suppressed.Subsequently, the zero point of the third phase (T phase) source voltageis detected at a time ¼ of a cycle after an energizing time of the firstphase (R phase), so that the third phase (T phase) is energized at anelectrical phase angle of the third phase (T phase) within the 40-to-80degree range, preferably within the 50-to-70 degree range. At thistiming, the magnetic fluxes of the S and T phases (half the magneticflux of the R phase and having an opposite sign), generated by thecurrent flowing in the S and T phases produced by the magnetic flux ofthe R phase which is energized first, are equal to the steady statemagnetic flux generated in the T phase when the T phase is energized.Therefore, the transient phenomena can be suppressed and the excitinginrush current of the third phase (T phase) can also be suppressed.

The voltage of each phase at this time and the flux of each phase afterenergizing are shown in FIG. 5. Finally, at any time after the thirdphase (T phase) is energized, the second phase (S phase) is energized.It is one of the features of the invention that this 3rd energizationcan be performed at any time. Because, the magnetic flux of the S phase,which is generated by the current flowing in the S phase created by themagnetic flux produced in the R and T phases, is made equal to thesteady state magnetic flux generated in the S phase when the S phase isenergized, no matter what any time the energizing of the S phase isperformed, both the transient phenomena and the exciting inrush currentof the second phase (S phase) can be suppressed. Generally, theenergization is set at an electrical phase angle of the S phase near0-120 degrees where discharge is unlikely.

Embodiment 5

Using the synchronous switching apparatus of this embodiment accordingto a fifth embodiment of the present invention, by the method ofdetecting each phase voltage, when in another case a three phase coretransformer or shunt reactor having star connected windings with aneutral point grounded is energized with a source voltage first, thezero point of the first phase (R phase) source voltage is detected, sothat the first phase (R phase) is energized at an electrical phase angleof the first phase (R phase) within the 70-to-110 degree range,preferably within a 80-to-100 degree range.

Accordingly, transient phenomena can be suppressed and the excitinginrush current of the first phase (R phase) can also be suppressed.

Subsequently, the zero point of the second phase (S phase) sourcevoltage is detected at a time ¼ of a cycle after an energizing time ofthe first phase (R phase), so that the second phase (S phase) isenergized at an electrical phase angle of the second phase (S phase)within the range of from −50 to −20 degrees, preferably within the rangeof from −40 to −20 degrees. At this timing, the magnetic fluxes of the Sand T phases (half of the magnetic flux of the R phase and oppositesign), generated by the currents flowing in the S and T phases producedby the magnetic flux created in the R phase first energized are equal tothe steady state magnetic flux generated in the S phase when the S phaseis energized. Therefore, the transient phenomena can be suppressed andthe exciting inrush current of the second phase (S phase) can also besuppressed.

Finally, at any time after the energizing of the second phase (S phase),the third phase (T phase) is energized. As already described, it is oneof the features of the invention that this third energization can beperformed at any time. Because, the magnetic flux of the T phase,generated by the current flowing in the T phase created by the magneticfluxes produced in the R and S phases, is equal to the steady statemagnetic flux generated in the T phase when the T phase is energized.Therefore, even if the energizing of the T phase is done at any timing,transient phenomena can be suppressed and the exciting inrush current ofthe third phase (T phase) can also be suppressed.

Embodiment 6

Using the synchronous switching apparatus of this embodiment accordingto a sixth embodiment of the present invention, by the method ofdetecting each phase-to-phase voltage, where a three phase coretransformer or shunt reactor having star connected windings with aneutral point grounded is energized with a source voltage first, thezero point of the first-to-second phase (R-to-S phase) voltage isdetected, so that the first phase (R phase) is energized at anelectrical phase angle of the first-to-second phase (R-to-S phase)voltage within the 40-to-80 degree range, preferably within the 50-to-70degree range. Accordingly, transient phenomena can be suppressed and theexciting inrush current of the first phase (R phase) can also besuppressed.

Subsequently, the zero point of the third-to-first phase (T-to-R phase)voltage is detected at a time ⅓ of a cycle after an energizing time ofthe first phase (R phase), so that the third phase (T phase) isenergized at an electrical phase angle of the third-to-first phase(T-to-R phase) voltage within the 10-to-50 degree range, preferablywithin the 20-to-40 degree range. Finally, the second phase (S phase) isenergized at any time after the energizing of the third phase (T phase).

Embodiment 7

Using the synchronous switching apparatus of this embodiment accordingto a seventh embodiment of the present invention, by the method ofdetecting each phase-to-phase voltage, when a three phase coretransformer or shunt reactor having star connected windings with aneutral point grounded is energized with a source voltage first, thezero point of the first-to-second phase (R-to-S phase) voltage isdetected, so that the first phase (R phase) is energized at anelectrical phase angle of the first-to-second phase (R-to-S phase)voltage within the 40-to-80 degree range, preferably within the 50-to-70degree range. Accordingly, transient phenomena can be suppressed and theexciting inrush current of the first phase (R phase) can also besuppressed.

Subsequently, the zero point of the second-to-third phase (S-to-T phase)voltage is detected at a time ⅓ of a cycle after an energizing time ofthe first phase (R phase), so that the second phase (S phase) isenergized at an electrical phase angle of the second-to-third phase(S-to-T phase) voltage within the range of from −80 to −40 degrees,preferably within the range of from −70 to −50 degrees. Finally, thesecond phase (S phase) is energized at any time after the energizing ofthe third phase (T phase).

Embodiment 8

Using the synchronous switching apparatus of this embodiment accordingto an eighth embodiment of the present invention, by the method ofdetecting each phase voltage, when three phase core transformer or shuntreactor having star connected windings with a neutral point ungrounded,or a single phase or three phase core delta connection transformer orshunt reactor is energized with a source voltage, the second phase (Sphase) is energized at any time.

With the neutral point ungrounded, energizing of one phase does notcause transient phenomena because a current path is not formed betweenthe phases. Energizing is generally set near an electrical phase angleof the 0-to-120 degree range in which it is difficult for discharge tooccur. Then, after the energizing of the second phase (S phase), thezero point of the first phase (R phase) source voltage is detected, sothat first phase (R phase) is energized at an electrical phase angle ofthe first phase (R phase) within the 100-to-140 degree range, preferablywithin the 110-to-130 degree range. Although a current path is formedbetween the R and S phases at this time, the R-to-S phase voltage is atits peak at this timing, so the magnetic flux generated in the R phaseis in the steady state and transient phenomena do not occur. Finally,the zero point of the third phase (T phase) source voltage is detectedat a time ⅓ of a cycle after the energizing time of the first phase (Rphase), the third phase (T phase) is energized at an electrical phaseangle of the third phase (T phase) within the 70-to-110 degree range,preferably within 80-to-100 degree range. At this timing, the magneticfluxes of the S and T phases (half the magnetic flux of the R phase andopposite sign), generated by the currents flowing in the S and T phasescreated by the magnetic flux generated between R and S phases, is madeequal to the steady state magnetic flux generated in the T phase whenthe T phase is energized. Thus, transient phenomena can be suppressedand the exciting inrush current of the third phase (T phase) can besuppressed.

Embodiment 9

Using the synchronous switching apparatus of this embodiment accordingto a ninth embodiment of the present invention, by the method ofdetecting each phase voltage, when a three-phase core transformer orshunt reactor having star connected windings with a neutral pointungrounded, or a single-phase and three-phase ore delta connectiontransformer or shunt reactor is energized with a source voltage, first,the first phase (R phase) is energized at any time. With the neutralpoint ungrounded, energizing of one phase does not cause transientphenomena because a current path is not formed between the phases.

Energizing is generally set near at an electrical phase angle of the0-to-120 degree range in which discharge is difficult to occur, as shownin FIG. 4. Then, after the energizing of the first phase (R phase), thezero point of the second phase (S phase) source voltage is detected, andthe second phase (S phase) is energized at an electrical phase angle ofthe second phase (S phase) within the range of from −140 to 100 degrees,preferably within the range of from −130 to −110 degrees. Although acurrent path is formed between the R and S phases at this time, theR-to-S phase voltage is at its peak at this timing, and so the magneticflux generated in the R phase is in the steady state and transientphenomena do not occur.

Finally, the zero point of the third phase (T phase) source voltage isdetected at a time ⅓ of a cycle after the energizing time of the secondphase (S phase), and the third phase (T phase) is energized at anelectrical phase angle of the third phase (T phase) within the 70-to-110degree range, preferably within 80-to-100 degree range. At this timing,the magnetic fluxes of the S and T phases (half the magnetic flux of theR phase and opposite sign), generated by the currents flowing in the Sand T phases created by the magnetic flux generated between R and Sphases, is made equal to the steady state magnetic flux generated in theT phase when the T phase is energized. Therefore, transient phenomenacan be suppressed and the exciting inrush current of the third phase (Tphase) can be suppressed.

Embodiment 10

Using the synchronous switching apparatus of this embodiment accordingto a tenth embodiment of the present invention, by the method ofdetecting each phase-to-phase voltage, when a three-phase coretransformer or shunt reactor having star-connected windings with aneutral point ungrounded, or a single phase and three-phase core deltaconnection transformer or shunt reactor are energized with a sourcevoltage, first, the second phase (S phase) is energized at any time.Then, after the energizing of the second phase (S phase), the zero pointof the first-to-second phase (R-to-S phase) voltage is detected, so thatthe first phase (R phase) is energized at an electrical phase angle ofthe first-to-second phase (R-to-S phase) voltage within the 70-to-110degree range, preferably within the 80-to-100 degree range.

Accordingly, transient phenomena can be suppressed and the excitinginrush current of the first phase (R phase) can be suppressed.Subsequently, the zero point of the third-to-first phase (T-to-R phase)voltage is detected at a time ⅓ of a cycle after the energizing time ofthe first phase (R phase), so that the third phase (T phase) isenergized at an electrical phase angle of the third-to-first phase(T-to-R phase) voltage within the 40-to-80 degree range, preferablywithin 50-to-70 degree range. At this timing, transient phenomena do notoccur in the T phase.

Embodiment 11

Using the synchronous switching apparatus of this embodiment accordingto an eleventh embodiment of the present invention, by the method ofdetecting each phase-to-phase voltage, when a three-phase coretransformer (or shunt reactor) having star-connected windings with aneutral point ungrounded, or a single-phase and three-phase core deltaconnection transformer or shunt reactor are energized with a sourcevoltage, first, the first phase (R phase) is energized at any time.Then, after the energizing of the first phase (R phase), the zero pointof the second-to-third phase (S-to-T phase) voltage is detected, so thatthe second phase (S phase) is energized at an electrical phase angle ofthe second-to-third phase (S-to-T phase) voltage within the range offrom −170 to −130 degrees, preferably within the 160-to-140 degreerange. Accordingly, transient phenomena can be suppressed and theexciting inrush current of the first phase (R phase) can be suppressed.Subsequently, the zero point of the third-to-first phase (T-to-R phase)voltage is detected at a time ⅓ of a cycle after the energizing time ofthe first phase (R phase), so that the third phase (T phase) isenergized at an electrical phase angle of the third-to-first phase(T-to-R phase) voltage within the 40-to-80 degree range, preferablywithin the 50-to-70 degree range. At this timing, transient phenomena donot occur in the T phase.

Embodiment 12

Next, the synchronous circuit breaker according to embodiment 12 of theinvention and its operation will be explained. The synchronous circuitbreaker and its operating sequence of this embodiment are the same asshown in FIGS. 1, 2 and 3 which have been described in theabove-mentioned embodiments.

When system equipment is energized by using a synchronous switchingapparatus configured in this way, first the transformers (5 a), (5 b)and (5 c) used for detecting the source voltage of R, S and T phases,respectively, detect the zero points of the source voltage of the R, Sand T phases. At the same time, the measuring transformers (5 d), (5 e)and (5 f) used for measuring R-to-S, S-to-T and T-to-R phase voltage,respectively and detect the zero voltage points of the R-to-S, S-to-Tand T-to-R phase voltage respectively. The phase control device 42estimates “a pole-closing time Tc” which is the time until an electricalphase angle of a certain ideal angular phase is reached, based on theoperating time as determined from the temperature, operating voltagesand past operating history, and adjusts “the delay time Td” foroutputting a closing signal such that closing may be established at aclosing time Ta corresponding to the target electrical phase angle foreach of the R, S and T phases, or at the closing time Ta correspondingto the target electrical phase angle of each of the R-to-S, S-to-T andT-to-R phase voltage, and provides a closing command to each of theswitching mechanisms (2 a), (2 b), and (2 c). When the switchingequipment is closed for the transformer (3) at the predetermined closingtime according to this command, transient phenomena can be suppressed,in principle.

Ideal energizing timing for system equipment such as transmission linesand capacitor banks is at the peak voltage or zero point of eachphase-to-phase voltage, but not at an electrical phase angle of thesource voltage of each phase. Therefore, more accurate closing can berealized by detecting not only the zero voltage point of the sourcevoltage of each of the R, S and T phases but also the zero voltage pointof each of the R-to-S, S-to-T and T-to-R phase voltage to determine theclosing time. Also, because the closing time of switching equipmentinevitably varies due to the variations in the mechanicalcharacteristics of the switching equipment and the occurrence ofdischarge, ideal closing is not always realized.

These variations in closing time are on the order of ±0.5 ms inswitching devices with high closing speed, and on the order of ±1.0 msin the switching devices of low-speed closing. The closing timevariations of ±0.5 ms and ±1.0 ms correspond to ±10 and ±20 degrees incommercial frequency, respectively. When the real energizing timing for.system equipment such as transmission lines and capacitor banks deviatesfrom an ideal energizing phase angle by the order of ±10 degrees (about±0.5 ms from the ideal closing time), the surge voltage and excitinginrush current may rise up to about the surge level which can besuppressed by the switching device of the resistor insertion system.This level can be allowable in practical use.

Therefore, the present embodiment can provide a switching apparatuswherein the variations in the closing time thereof can be controlled towithin ±10 degrees (less than ±0.5 ms from a predetermined closingtime).

When this embodiment is applied to a switching apparatus with lowclosing speed, the real closing can deviate from the ideal closing phaseangle by about ±20 degrees (about ±1.0 ms from the ideal closing time).Thereby, the surge voltage or inrush current occurred can be, atmaximum, half of the surge level generated by the switching devices inwhich the closing phases are not controlled.

In systems where these surge levels are problems in practical use, byusing the surge absorber(15) provided between each of the R, S, and Tphases and ground for suppressing over-voltages and the surgeabsorbers(16) for suppressing R-to-S, S-to-T and T-to-R phaseover-voltages, the transient phenomena can be suppressed to minimizevoltage disturbances in each of the R, S, and T phase voltage and ineach of the R-to-S, S-to-T and T-to-R phase voltage.

Further, each of the surge absorber (15), (16) can suppress transientphenomena caused by switching of other switching equipment to improvethe zero point detection accuracy and hence energizing accuracy.

Embodiment 13

More specification, using the synchronous switching apparatus of thepresent embodiment according to the sequence of claim 12, by the methodof detecting each of the phase voltage, capacitor banks with a neutralpoint grounded or transmission lines without trapped charge areenergized with a source voltage, first, the zero point of the firstphase (R phase) source voltage is detected, so that the first phase (Rphase) is energized at an electrical phase angle of the first phase (Rphase) within the range of from −20 to 20 degrees, preferably within therange of from −10 to 10 degrees. At this timing, the voltage applied tothe R phase is zero or small, so that transient currents are notgenerated. Also, when the energizing electrical phase angle becomes aslarge as 0 ±20 degrees, the surge absorber (15 a) provided between thebus (10 a) for the R phase and ground for suppressing over-voltages andthe surge absorbers (16) for suppressing the R-to-S, S-to-T and T-to-Rphase over-voltages can suppress the transient phenomena.

Next, the zero point of the third phase (T phase) source voltage isdetected at a time ⅓ of a cycle after the energizing time of the firstphase (R phase), and the third phase (T phase) is energized at anelectrical phase angle of the third phase (T phase) within the range offrom −20 to 20 degrees, preferably within the range of from −10 to 10degrees. At this timing, the voltage applied to the T phase is zero orsmall, so that transient currents can not be generated. Also, when theelectrical phase angle becomes as large as 0 ±20 degrees, the surgeabsorber (15 b) provided between the bus (10 c) for the R phase andground for suppressing over-voltages and the surge absorbers (16) forsuppressing the phase-to-phase over-voltages can suppress the transientphenomena.

Finally, the zero point of the second phase (S phase) source voltage isdetected at a time ⅓ of a cycle after the energizing time of the thirdphase (T phase), and the second phase (S phase) is energized at anelectrical phase angle of the second phase (S phase) within the range offrom −20 to 20 degrees, preferably within the range of from −10 to 10degrees. At this timing, the voltage applied to the S phase is zero orsmall, so that transient currents can not be generated. Also, when theelectrical phase angle becomes as large as 0 ±20 degrees, the transientphenomena can be suppressed by the surge absorber (15 b) providedbetween the bus (10 b) for the S phase and ground for suppressingover-voltages and the surge absorbers (16) for suppressing thephase-to-phase over-voltages.

Embodiment 14

Using the synchronous switching apparatus of the present embodimentaccording to the sequence of claim 13, by the method of detecting eachphase-to-phase voltage, when capacitor banks with a neutral pointgrounded or transmission lines without trapped charge are energized witha source voltage, first, the zero point of the first-to-second phase(R-to-S phase) voltage is detected, so that the first phase (R phase) isenergized at an electrical phase angle of the first-to-second phase(R-to-S phase) voltage within the range of from −50 to −10 degrees,preferably within the range of from −40 to −20 degrees. At this timing,the voltage applied to the R phase is zero or small, so that transientcurrents are not generated. Also, when the energizing electrical phaseangle becomes as large as −30 ±20 degrees, the transient phenomena canbe suppressed by the surge absorber (15 a) provided between the bus (10a) for the R phase and ground for suppressing over-voltages and thesurge absorbers (16) for suppressing each of the R-to-S, S-to-T andT-to-R phase over-voltages.

Next, the zero point of the third-to-first phase (T-to-R phase) voltageis detected at a time ⅓ of a cycle after the energizing time of thefirst phase (R phase), and the third phase (T phase) is energized at anelectrical phase angle of the third-to-first phase (T-to-R phase)voltage within the range of from −50 to −10 degrees, preferably withinthe range of from −40 to −20 degrees. At this timing, the voltageapplied to the T phase is zero or small, so that transient currents cannot be generated. Also, when the electrical phase angle becomes as largeas −30 ±20 degrees, the transient phenomena can be suppressed by thesurge absorber(15 c) provided between the bus (10 c) for the T phase andground for suppressing over-voltages and the surge absorbers (16) forsuppressing the phase-to-phase over-voltages. Finally, the zero point ofthe second-to-third phase (S-to-T phase) voltage is detected at a time ⅓of a cycle after the energizing time of the third phase (T phase), andthe second phase (S phase) is energized at an electrical phase angle ofthe second-to-third phase (S-to-T phase) voltage within the range offrom −50 to 10 degrees, preferably within the range of from −40 to −20degrees.

At this timing, the voltage applied to the S phase is zero or small, sothat the transient currents can not be created. Also, when theenergizing electrical phase angle becomes as large as 0 ±20 degrees, thetransient phenomena can be suppressed by the surge absorber (15 b)provided between the bus for the S phase (10 b) and ground forsuppressing over-voltages and the surge absorbers (16) for suppressingthe phase-to-phase over-voltages.

Embodiment 15

Using the synchronous switching apparatus of the invention according tothe sequence of claim 14, by the method of detecting each of the phasevoltage, when capacitor banks with a neutral point ungrounded areenergized with a source voltage, first, the first phase (R) is energizedat any time.

With the neutral point ungrounded, energizing of one phase does notcause the transient phenomena because a current path is not formedbetween the phases. Energizing is generally set near at the peak or inthe 0-to-120 degree range of the electrical phase angle of the R phasein which discharge is difficult to occur. Then, after the energizing ofthe first phase (R phase), the zero point of the third phase (T phase)source voltage is detected, and the third phase (T phase) is energizedat an electrical phase angle of the third phase (T phase) within the10-to-50 degree range, preferably within the 20-to-40 degree range. Atthis time, a current path is formed between the R and S phases, butbecause the T-to-R phase voltage is zero or small, transient currentscan not be created.

Also, when the energizing electrical phase angle becomes as large as 30±20 degrees, the surge absorbers (16) for suppressing the phase-to-phaseover-voltages can suppress the transient phenomena.

Finally, the zero point of the second phase (S phase) source voltage isdetected at a time ¼ of a cycle after the energizing time of the thirdphase (T phase), and the second phase (S phase) is energized at anelectrical phase angle of the second phase (S phase) within the range offrom −20 to 20 degrees, preferably within the range of from −10 to 10degrees. The voltage applied to the S phase at this time is zero orsmall, so that the transient currents can not be created. Also, when theenergizing electrical phase angle becomes as large as 0 ±20 degrees, thesurge absorbers (16) for suppressing the phase-to-phase over-voltagescan suppress the transient phenomena.

Embodiment 16

Using the synchronous switching apparatus of the present embodimentaccording to the sequence of claim 15, by the method of detecting eachof the phase voltage, when capacitor banks with a neutral pointungrounded are energized with a source voltage, first, the second phase(S phase) is energized at any time. Then, after the energizing of thesecond phase (S phase), the zero point of the first phase (R phase)source voltage is detected, so that the first phase (R phase) isenergized at an electrical phase angle of the first phase (R phase)within the 10-to-50 degree range, preferably within the 20-to-40 degreerange. At this timing, a current path is formed between the R and Sphases, but then the R-to-S phase voltage is zero or small, so that thetransient currents can not be created. Also, when the energizingelectrical phase angle becomes as large as 30 ±20 degrees, the surgeabsorbers (16) for suppressing the phase-to-phase over-voltages cansuppress the transient phenomena.

Finally, the zero point of the third phase (T phase) source voltage isdetected at a time ¼ of a cycle after the energizing time of the firstphase (R phase), and the third phase (T phase) is energized at anelectrical phase angle of the third phase (T phase) within the range offrom −20 to 20 degrees, preferably within the range of from −10 to 10degrees. Also, when the energizing electrical phase angle becomes aslarge as 0 ±20 degrees, the surge absorbers(16) for suppressing thephase-to-phase over-voltages can suppress the transient phenomena.

Embodiment 17

Using the synchronous switching apparatus of the invention according tothe sequence of claim 16, by the method of detecting each of the phasevoltage, when capacitor banks with a neutral point ungrounded areenergized with a source voltage, first, the third phase (T phase) isenergized at any time. Then, after the energizing of the third phase (Tphase), the zero point of the second phase (S phase) source voltage isdetected, so that the second phase (S phase) is energized at anelectrical phase angle of the second phase (S phase) within the 10-to-50degree range, preferably within the 20-to-40 degree range. At thistiming, a current path is formed between the S and T phases, but thenthe S-to-T phase voltage is zero or small, so that the transientcurrents can not be created. Also, when the energizing electrical phaseangle becomes as large as 30 ±20 degrees, the surge absorbers (16) forsuppressing the phase-to-phase over-voltages can suppress the transientphenomena.

Finally, the zero point of the first phase (R phase) source voltage isdetected at the time ¼ of a cycle after the energizing time of thesecond phase (S phase), and the first phase (R phase) is energized at anelectrical phase angle of the first phase (R phase)within the range offrom −20 to 20 degrees, preferably within the range of from −10 to 10degrees. Also, when the energizing electrical phase angle becomes aslarge as 0 ±20 degrees, the surge absorbers (16) for suppressing thephase-to-phase over-voltages can suppress the transient phenomena.

Embodiment 18

Using the synchronous switching apparatus of the present embodimentaccording to the sequence described in claim 17, by the method ofdetecting each of the phase voltage, when capacitor banks with a neutralpoint ungrounded are energized with a source voltage, first, the firstphase (R phase) is energized at any time. With the neutral pointungrounded, energizing of one phase does not cause transient phenomenabecause a current path is not formed between the phases. Energizing isgenerally set near at the peak or near in the 0-to-120 degree range ofthe electrical phase angle of the R phase in which discharge isdifficult to occur. Then, after the energizing of the first phase (Rphase), the zero point of the third-to-first phase (T-to-R phase)voltage is detected, so that the third phase (T phase) is energized atan electrical phase angle of the third-to-first phase (T-to-R phase)voltage within the range of from −20 to 20 degrees, preferably withinthe range of from −10 to 10 degrees. At this timing, a current path isformed between the T and R phases, but then the T-to-R phase voltage iszero or small, so that the transient currents can not be created. Also,when the energizing electrical phase angle becomes as large as 0 ±20degrees, the surge absorbers (16) for suppressing the phase-to-phaseover-voltages can suppress the transient phenomena.

Finally, the zero point of the second-to-third phase (S-to-T phase)voltage is detected at a time ¼ of a cycle after the energizing time ofthe third phase (T phase), and the second phase (S phase) is energizedat an electrical phase angle of the second-to-third phase (S-to-T phase)voltage within the range of from −50 to -10 degrees, preferably withinthe range of from −40 to 20 degrees. At this time, the voltage appliedto the S phase is zero or small, so that the transient currents can notbe created. Also, when the energizing electrical phase angle becomes aslarge as 30 ±20 degrees, the surge absorbers (16) for suppressing eachof the phase-to-phase over-voltages can suppress the transientphenomena.

Embodiment 19

Using the synchronous switching apparatus of the present embodimentaccording to the sequence of claim 18, by the method of detecting eachof the phase voltage, when capacitor banks with a neutral pointungrounded are energized with a source voltage, first, the second phase(S phase) is energized at any time. Then, after the energizing of thesecond phase (S phase), the zero point of the first-to-second phase(R-to-S phase) voltage is detected, so that the first phase (R phase) isenergized at an electrical phase angle of the first-to-second phase(R-to-S phase) voltage within the range of from −20 to 20 degrees,preferably within the range of from −10 to 10 degrees. At this timing, acurrent path is formed between the R and S phases, but then the R-to-Sphase voltage is zero or small, so that the transient currents can notbe created.

Also, when the energizing electrical phase angle becomes as large as 0±20 degrees, the surge absorbers (16) for suppressing the phase-to-phaseover-voltages can suppress the transient phenomena. Finally, the zeropoint of the third-to-first phase (T-to-R phase) voltage is detected ata time ¼ of a cycle after the energizing time of the first phase (Rphase), and the third phase (T phase) is energized at an electricalphase angle of the third-to-first phase (T-to-R phase) voltage withinthe range of from −50 to −10 degrees, preferably within the range offrom −40 to 20 degrees. Also, when the energizing electrical phase anglebecomes as large as −30 ±20 degrees, the surge absorbers (16) forsuppressing the phase-to-phase over-voltages can suppress the transientphenomena.

Embodiment 20

Using the synchronous switching apparatus of the present embodimentaccording to the sequence of claim 19, by the method of detecting eachof the phase voltage, when capacitor banks with a neutral pointungrounded are energized with a source voltage, first, the third phase(T phase) is energized at any time. Then, after the energizing of thethird phase (T phase), the zero point of the second-to-third phase(S-to-T phase) voltage is detected, so that the second phase (S phase)is energized at an electrical phase angle of the second-to-third phase(S-to-T phase) voltage within the range of from −20 to 20 degrees,preferably within the range of from −10 to 10 degrees. At this timing, acurrent path is formed between the S and T phases, but then the S-to-Tphase voltage is zero or small, so that the transient currents can notbe created. Also, when the energizing electrical phase angle becomes aslarge as 0 ±20 degrees, the surge absorbers (16) for suppressing thephase-to-phase over-voltages can suppress the transient phenomena.Finally, the zero point of the first-to-second phase (R-to-S phase)voltage is detected at a time ¼ of a cycle after the energizing time ofthe second phase (S phase), and the first phase (R phase) is energizedat an electrical phase angle of the first-to-second phase (R-to-S phase)voltage within the range of from −50 to −10 degrees, preferably withinthe range of from −40 to 20 degrees.

Also, when the energizing electrical phase angle becomes as large as −30±20 degrees, the surge absorbers (16) for suppressing the phase-to-phaseover-voltages can suppress the transient phenomena.

This embodiment provides closing timing which can suppress theoccurrence of transient inrush currents and surge voltages, and whichcan be realized by a switching device for each phase, even if realenergizing timing deviates from ideal energizing timing.

Industrial Applicability

The invention provides closing timing which can suppress the occurrenceof transient inrush currents and surge voltages, and which can berealized by switching equipment for each phase, even if the real closingtime of the switching device deviates from the ideal closing time due tothe mechanical characteristics of the switching device.

What is claimed is:
 1. A synchronous switching apparatus for use with amultiple phase power system having a plurality of phases and fordetecting a source voltage of each phase and energizing each phase at anelectrical phase angle predetermined for each phase, comprising: aplurality of switching devices, one switching device being provided foreach phase and opening and closing an impedance load; a plurality ofswitching mechanisms, closing and opening the switching devices; aplurality of voltage measuring transformers, measuring source voltagesof the phases; a plurality of phase-to-phase voltage measuringtransformers, measuring respective phase-to-phase voltages; and aplurality of phase control devices, one phase control device beingprovided for each phase and issuing a command to energize the impedanceload with a source voltage at an electrical phase angle in a rangepredetermined for the phase, in response to detection of a zero point ofa source voltage of the phase by the voltage measuring transformer or todetection of a zero point of the phase-to-phase voltage by thephase-to-phase voltage measuring transformer, wherein the synchronousswitching apparatus is adapted for use with an impedance load in theform of a single-phase core transformer or shunt reactor with a neutralpoint grounded, wherein: the plurality of phases comprises a first phase(R phase), a second phase (S phase), and a third phase (T phase); theplurality of voltage measuring transformers comprises a first, a second,and a third voltage measuring transformer, measuring source voltages ofthe first, second, and third phases, respectively; and the predeterminedelectrical phase angles of each of the first, second, and third phasesare within a range of 90 degrees (voltage peak value of the R, S, and Tphases) ±20 degrees, wherein, the impedance load is energized with asource voltage via a command sequence, wherein the phase control devicesrespectively issue a first command for energizing the first phase (Rphase) at the predetermined electrical phase angle of the first phase inresponse to detection of a zero point of a first phase (R phase) sourcevoltage by the first voltage measuring transformer, a second command forenergizing the third phase (T phase) at the predetermined electricalphase angle of the third phase in response to detection of a zero pointof a third phase (T phase) source voltage by the third voltage measuringtransformer at a time around ⅓ of a cycle after an energizing time ofthe first phase (R phase), and a third command for energizing the secondphase (S phase) at the predetermined electrical phase angle of thesecond phase in response to detection of a zero point of a second phase(S phase) source voltage by the second voltage measuring transformer ata time around ⅓ of a cycle after an energizing time of the third phase(T phase).
 2. A synchronous switching apparatus for use with a multiplephase power system having a plurality of phases and for detecting asource voltage of each phase and energizing each phase at an electricalphase angle predetermined for each phase, comprising: a plurality ofswitching devices, one switching device being provided for each phaseand opening and closing an impedance load; a plurality of switchingmechanisms, closing and opening the switching devices; a plurality ofvoltage measuring transformers, measuring source voltages of the phases;a plurality of phase-to-phase voltage measuring transformers, measuringrespective phase-to-phase voltages; and a plurality of phase controldevices, one phase control device being provided for each phase andissuing a command to energize the impedance load with a source voltageat an electrical phase angle in a range predetermined for the phase, inresponse to detection of a zero point of a source voltage of the phaseby the voltage measuring transformer or to detection of a zero point ofthe phase-to-phase voltage by the phase-to-phase voltage measuringtransformer, wherein the synchronous switching apparatus is adapted foruse with an impedance load in the form of a single-phase coretransformer or shunt reactor with a neutral point grounded, wherein: theplurality of phases comprises a first phase (R phase), a second phase (Sphase), and a third phase (T phase); the plurality of phase-to-phasevoltage measuring transformers comprises a first-to-second (R-to-Sphase), a second-to-third (S-to-T phase), and a third-to-first (T-to-Rphase) phase voltage measuring transformer, measuring a first-to-second,a second-to-third, and a third-to-first phase voltage, respectively; andthe predetermined electrical phase angles of each of the first-to-secondphase voltage, the second-to-third phase voltage, and the third-to-firstphase voltage are within a range of 60 degrees ±20 degrees, wherein, theimpedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first phase (R phase) at the predeterminedelectrical phase angle of the first-to-second phase (R-to-S phase)voltage in response to detection of a zero point of the first-to-secondphase (R-to-S phase) voltage by the first-to-second phase voltagemeasuring transformer, a second command for energizing the third phase(T phase) at the predetermined electrical phase angle of thethird-to-first phase (T-to-R phase) voltage in response to detection ofa zero point of the third-to-first phase (T-to-R phase) voltage by thethird-to-first phase voltage measuring transformer at a time around ⅓ ofa cycle after an energizing time of the first phase, and a third commandfor energizing the second phase (S phase) at the predeterminedelectrical phase angle of the second-to-third phase (S-to-T phase)voltage in response to detection of a zero point of the second-to-thirdphase (S-to-T phase) voltage by the second-to-third phase voltagemeasuring transformer at a time around ⅓ of a cycle after an energizingtime of the third phase (T phase).
 3. A synchronous switching apparatusfor use with a multiple phase power system having a plurality of phasesand for detecting a source voltage of each phase and energizing eachphase at an electrical phase angle predetermined for each phase,comprising: a plurality of switching devices, one switching device beingprovided for each phase and opening and closing an impedance load; aplurality of switching mechanisms, closing and opening the switchingdevices; a plurality of voltage measuring transformers, measuring sourcevoltages of the phases; a plurality of phase-to-phase voltage measuringtransformers, measuring respective phase-to-phase voltages; and aplurality of phase control devices, one phase control device beingprovided for each phase and issuing a command to energize the impedanceload with a source voltage at an electrical phase angle in a rangepredetermined for the phase, in response to detection of a zero point ofa source voltage of the phase by the voltage measuring transformer or todetection of a zero point of the phase-to-phase voltage by thephase-to-phase voltage measuring transformer, wherein the synchronousswitching apparatus is adapted for use with an impedance load in theform of a three-phase core transformer or shunt reactor havingstar-connected windings with a neutral point grounded, wherein: theplurality of phases comprises a first phase (R phase), a second phase (Sphase), and a third phase (T phase); the plurality of voltage measuringtransformers comprises a first and a third voltage measuringtransformer, measuring source voltages of the first and third phases,respectively; the predetermined electrical phase angle of the firstphase is within a range of 90 degrees (voltage peak value of the Rphase) ±20 degrees; and the predetermined electrical phase angle of thethird phase is within a range of 60 degrees ±20 degrees, wherein, theimpedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first phase (R phase) at the predeterminedelectrical phase angle of the first phase in response to detection of azero point of a first phase (R phase) source voltage by a first voltagemeasuring transformer, a second command for energizing the third phase(T phase) at the predetermined electrical phase angle of the third phasein response to detection of a zero point of a third phase (T phase)source voltage by the third voltage measuring transformer at a timearound ¼ of a cycle after an energizing time of the first phase (Rphase), and a third command for energizing the second phase (S phase) atany time after the energizing of the third phase (T phase).
 4. Asynchronous switching apparatus for use with a multiple phase powersystem having a plurality of phases and for detecting a source voltageof each phase and energizing each phase at an electrical phase anglepredetermined for each phase, comprising: a plurality of switchingdevices, one switching device being provided for each phase and openingand closing an impedance load; a plurality of switching mechanisms,closing and opening the switching devices; a plurality of voltagemeasuring transformers, measuring source voltages of the phases; aplurality of phase-to-phase voltage measuring transformers, measuringrespective phase-to-phase voltages; and a plurality of phase controldevices, one phase control device being provided for each phase andissuing a command to energize the impedance load with a source voltageat an electrical phase angle in a range predetermined for the phase, inresponse to detection of a zero point of a source voltage of the phaseby the voltage measuring transformer or to detection of a zero point ofthe phase-to-phase voltage by the phase-to-phase voltage measuringtransformer, wherein the synchronous switching apparatus is adapted foruse with an impedance load in the form of a single-phase coretransformer or shunt reactor with a neutral point grounded, wherein: theplurality of phases comprises a first phase (R phase), a second phase (Sphase), and a third phase (T phase); the predetermined electrical phaseangle of the first phase is within a range of 90 degrees (voltage peakvalue of the R phase) ±20 degrees; the predetermined electrical phaseangle of the second phase is within a range of −30 degrees ±20 degrees;and the plurality of voltage measuring transformers comprises a firstand a second voltage measuring transformer, measuring source voltages ofthe first and second phases, respectively, wherein, the impedance loadis energized with a source voltage via a command sequence, wherein thephase control devices respectively issue a first command for energizinga first phase (R phase) at the predetermined electrical phase angle ofthe first phase in response to detection of a zero point of the firstphase (R phase) source voltage by the first voltage measuringtransformer, a second command for energizing a second phase (S phase) atthe predetermined electrical phase angle of the second phase in responseto detection of a zero point of a second phase (S phase) source voltageby the second voltage measuring transformer at a time around ¼ of acycle after an energizing time of the first phase, and a third commandfor energizing a third phase (T phase) at any time after the energizingof the second phase (S phase).
 5. A synchronous switching apparatus foruse with a multiple phase power system having a plurality of phases andfor detecting a source voltage of each phase and energizing each phaseat an electrical phase angle predetermined for each phase, comprising: aplurality of switching devices, one switching device being provided foreach phase and opening and closing an impedance load; a plurality ofswitching mechanisms, closing and opening the switching devices; aplurality of voltage measuring transformers, measuring source voltagesof the phases; a plurality of phase-to-phase voltage measuringtransformers, measuring respective phase-to-phase voltages; and aplurality of phase control devices, one phase control device beingprovided for each phase and issuing a command to energize the impedanceload with a source voltage at an electrical phase angle in a rangepredetermined for the phase, in response to detection of a zero point ofa source voltage of the phase by the voltage measuring transformer or todetection of a zero point of the phase-to-phase voltage by thephase-to-phase voltage measuring transformer, wherein the synchronousswitching apparatus is adapted for use with an impedance load in theform of a single-phase core transformer or shunt reactor with a neutralpoint grounded, wherein: the plurality of phases comprises a first phase(R phase), a second phase (S phase), and a third phase (T phase); theplurality of phase-to-phase voltage measuring transformers comprises afirst-to-second (R-to-S phase) and a third-to-first (T-to-R phase) phasevoltage measuring transformer, measuring a first-to-second and athird-to-first phase voltage, respectively; the predetermined electricalphase angle of the first-to-second phase voltage is within a range of 60degrees ±20 degrees; and the predetermined electrical phase angle of thethird-to-first phase voltage is within a range of 30 degrees ±20degrees, wherein, the impedance load is energized with a source voltagevia a command sequence, wherein the phase control devices respectivelyissue a first command for energizing the first phase (R phase) at thepredetermined electrical phase angle of the first-to-second phase(R-to-S phase) voltage in response to detection of a zero point of thefirst-to-second phase (R-to-S phase) voltage by the first-to-secondphase voltage measuring transformer, a second command for energizing thethird phase (T phase) at the predetermined electrical phase angle of thethird-to-first phase (T-to-R phase) voltage in response to detection ofa zero point of a third-to-first phase (T-to-R phase) voltage by thethird-to-first phase voltage measuring transformer at a time around ⅓ ofa cycle after an energizing time of the first phase (R phase), and athird command for energizing a second phase (S phase) at any time afterthe energizing of the third phase (T phase).
 6. A synchronous switchingapparatus for use with a multiple phase power system having a pluralityof phases and for detecting a source voltage of each phase andenergizing each phase at an electrical phase angle predetermined foreach phase, comprising: a plurality of switching devices, one switchingdevice being provided for each phase and opening and closing animpedance load; a plurality of switching mechanisms, closing and openingthe switching devices; a plurality of voltage measuring transformers,measuring source voltages of the phases; a plurality of phase-to-phasevoltage measuring transformers, measuring respective phase-to-phasevoltages; and a plurality of phase control devices, one phase controldevice being provided for each phase and issuing a command to energizethe impedance load with a source voltage at an electrical phase angle ina range predetermined for the phase, in response to detection of a zeropoint of a source voltage of the phase by the voltage measuringtransformer or to detection of a zero point of the phase-to-phasevoltage by the phase-to-phase voltage measuring transformer, wherein thesynchronous switching apparatus is adapted for use with an impedanceload in the form of a three-phase core transformer or shunt reactorhaving star-connected windings with a neutral point grounded, wherein:the plurality of phases comprises a first phase (R phase), a secondphase (S phase), and a third phase (T phase); the plurality ofphase-to-phase voltage measuring transformers comprises afirst-to-second (R-to-S phase), and a second-to-third (S-to-T phase),measuring a first-to-second and a second-to-third phase voltage,respectively; and the predetermined electrical phase angle of thefirst-to-second phase voltage is within a range of 60 degrees ±20degrees; and the predetermined electrical phase angle of thesecond-to-third phase voltage is within a range of −60 degrees ±20degrees, wherein the impedance load is energized with a source voltagevia a command sequence, wherein the phase control devices respectivelyissue a first command for energizing the first phase (R phase) at thepredetermined electrical phase angle of the first-to-second phase(R-to-S phase) voltage in response to detection of a zero point of thefirst-to-second phase (R-to-S phase) voltage by the first-to-secondphase voltage measuring transformer, a second command for energizing thesecond phase (T phase) at the predetermined electrical phase angle ofthe second-to-third phase (S-to-T phase) voltage in response todetection of a zero point of the second-to-third phase (S-to-T phase)voltage by the second-to-third phase voltage measuring transformer at atime around ⅓ of a cycle after an energizing time of the first phase (Rphase), and a third command for energizing the third phase (T phase) atany time after the energizing of the second phase (S phase).
 7. Asynchronous switching apparatus for use with a multiple phase powersystem having a plurality of phases and for detecting a source voltageof each phase and energizing each phase at an electrical phase anglepredetermined for each phase, comprising: a plurality of switchingdevices, one switching device being provided for each phase and openingand closing an impedance load; a plurality of switching mechanisms,closing and opening the switching devices; a plurality of voltagemeasuring transformers, measuring source voltages of the phases; aplurality of phase-to-phase voltage measuring transformers, measuringrespective phase-to-phase voltages; and a plurality of phase controldevices, one phase control device being provided for each phase andissuing a command to energize the impedance load with a source voltageat an electrical phase angle in a range predetermined for the phase, inresponse to detection of a zero point of a source voltage of the phaseby the voltage measuring transformer or to detection of a zero point ofthe phase-to-phase voltage by the phase-to-phase voltage measuringtransformer, wherein the synchronous switching apparatus is adapted foruse with an impedance load in the form of a three-phase core transformeror shunt reactor having star-connected windings with a neutral pointungrounded, or a delta connection transformer or shunt reactor, wherein:the plurality of phases comprises a first phase (R phase), a secondphase (S phase), and a third phase (T phase); the plurality of voltagemeasuring transformers comprises a first and a third voltage measuringtransformer, measuring source voltages of the first and third phases,respectively; the predetermined electrical phase angle of the firstphase is within a range of 120 degrees ±20 degrees; and thepredetermined electrical phase angle of the third phase is within arange of 90 degrees ±20 degrees; wherein, the impedance load isenergized with a source voltage via a command sequence, wherein thephase control devices respectively issue a first command for energizingthe second phase (S phase) at any time, a second command for energizingthe first phase (R phase) at the predetermined electrical phase angle ofthe first phase (R phase) in response to detection of a zero point of afirst (R phase) source voltage by the first voltage measuringtransformer after the energizing of the second phase (S phase), and athird command for energizing the third phase (T phase) at thepredetermined electrical phase angle of the third phase (T phase) inresponse to detection of a zero point of a third phase (T phase) sourcevoltage by the third voltage measuring transformer at a time around ⅓ ofa cycle after an energizing time of the first phase (R phase).
 8. Asynchronous switching apparatus for use with a multiple phase powersystem having a plurality of phases and for detecting a source voltageof each phase and energizing each phase at an electrical phase anglepredetermined for each phase, comprising: a plurality of switchingdevices, one switching device being provided for each phase and openingand closing an impedance load; a plurality of switching mechanisms,closing and opening the switching devices; a plurality of voltagemeasuring transformers, measuring source voltages of the phases; aplurality of phase-to-phase voltage measuring transformers, measuringrespective phase-to-phase voltages; and a plurality of phase controldevices, one phase control device being provided for each phase andissuing a command to energize the impedance load with a source voltageat an electrical phase angle in a range predetermined for the phase, inresponse to detection of a zero point of a source voltage of the phaseby the voltage measuring transformer or to detection of a zero point ofthe phase-to-phase voltage by the phase-to-phase voltage measuringtransformer, wherein the synchronous switching apparatus is adapted foruse with an impedance load in the form of a three-phase core transformeror shunt reactor having star-connected windings with a neutral pointungrounded, or a single-phase core and three-phase core delta connectiontransformer or shunt reactor, wherein: the plurality of phases comprisesa first phase (R phase), a second phase (S phase), and a third phase (Tphase); the plurality of voltage measuring transformers comprises asecond and a third voltage measuring transformer, measuring sourcevoltages of the second and third phases, respectively; the predeterminedelectrical phase angle of the second phase is within a range of −120degrees ±20 degrees; and the predetermined electrical phase angle of thethird phase is within a range of 90 degrees ±20 degrees; wherein, theimpedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first phase (R phase) at any time, a secondcommand for energizing the second phase (S phase) at the predeterminedelectrical phase angle of the second phase (S phase) in response todetection of a zero point of a second phase (S phase) source voltage bythe second voltage measuring transformer after the energizing of thefirst phase (R phase), and a third command for energizing the thirdphase (T phase) at the predetermined electrical phase angle of the thirdphase (T phase) in response to detection of a zero point of a thirdphase (T phase) source voltage at a time around ⅓ of a cycle after anenergizing time of the second phase (S phase).
 9. A synchronousswitching apparatus for use with a multiple phase power system having aplurality of phases and for detecting a source voltage of each phase andenergizing each phase at an electrical phase angle predetermined foreach phase, comprising: a plurality of switching devices, one switchingdevice being provided for each phase and opening and closing animpedance load; a plurality of switching mechanisms, closing and openingthe switching devices; a plurality of voltage measuring transformers,measuring source voltages of the phases; a plurality of phase-to-phasevoltage measuring transformers, measuring respective phase-to-phasevoltages; and a plurality of phase control devices, one phase controldevice being provided for each phase and issuing a command to energizethe impedance load with a source voltage at an electrical phase angle ina range predetermined for the phase, in response to detection of a zeropoint of a source voltage of the phase by the voltage measuringtransformer or to detection of a zero point of the phase-to-phasevoltage by the phase-to-phase voltage measuring transformer, wherein thesynchronous switching apparatus is adapted for use with an impedanceload in the form of a three-phase core transformer or shunt reactorhaving star-connected windings with a neutral point ungrounded, or asingle-phase core and three-phase core delta connection transformer orshunt reactor, wherein: the plurality of phases comprises a first phase(R phase), a second phase (S phase), and a third phase (T phase); theplurality of phase-to-phase voltage measuring transformers comprises afirst-to-second (R-to-S phase) and a third-to-first (T-to-R phase) phasevoltage measuring transformer, measuring a first-to-second and athird-to-first phase voltage, respectively; the predetermined electricalphase angle of the first-to-second phase voltage is within a range of 90degrees ±20 degrees; and the predetermined electrical phase angle of thethird-to-first phase voltage is within a range of 60 degrees ±20degrees, wherein, the impedance load is energized with a source voltagevia a command sequence, wherein the phase control devices respectivelyissue a first command for energizing the second phase (S phase) at anytime, a second command for energizing the first phase (R phase) at thepredetermined electrical phase angle of a first-to-second phase (R-to-Sphase) voltage in response to detection of a zero point of afirst-to-second phase (R-to-S phase) voltage by the first-to-secondphase voltage measuring transformer after an energizing time of thesecond phase (S phase), and a third command for energizing the thirdphase (T phase) at the predetermined electrical phase angle of athird-to-first phase (T-to-R phase) voltage in response to detection ofa zero point of a third-to-first phase (T-to-R phase) voltage by thethird-to-first phase voltage measuring transformer at a time around ⅓ ofa cycle after an energizing time of the first phase (R phase).
 10. Asynchronous switching apparatus for use with a multiple phase powersystem having a plurality of phases and for detecting a source voltageof each phase and energizing each phase at an electrical phase anglepredetermined for each phase, comprising: a plurality of switchingdevices, one switching device being provided for each phase and openingand closing an impedance load; a plurality of switching mechanisms,closing and opening the switching devices; a plurality of voltagemeasuring transformers, measuring source voltages of the phases; aplurality of phase-to-phase voltage measuring transformers, measuringrespective phase-to-phase voltages; and a plurality of phase controldevices, one phase control device being provided for each phase andissuing a command to energize the impedance load with a source voltageat an electrical phase angle in a range predetermined for the phase, inresponse to detection of a zero point of a source voltage of the phaseby the voltage measuring transformer or to detection of a zero point ofthe phase-to-phase voltage by the phase-to-phase voltage measuringtransformer, wherein the synchronous switching apparatus is adapted foruse with an impedance load in the form of a three-phase core transformeror shunt reactor having star-connected windings with a neutral pointungrounded, or a single-phase core and three-phase core delta connectiontransformer or shunt reactor, wherein: the plurality of phases comprisesa first phase (R phase), a second phase (S phase), and a third phase (Tphase); the plurality of phase-to-phase voltage measuring transformerscomprises a second-to-third (S-to-T phase) and a third-to-first (T-to-Rphase) phase voltage measuring transformer, measuring a second-to-thirdand a third-to-first phase voltage, respectively; the predeterminedelectrical phase angle of the second-to-third phase voltage is within arange of −150 degrees ±20 degrees; and the predetermined electricalphase angle of the third-to-first phase voltage is within a range of 60degrees ±20 degrees, wherein, the impedance load is energized with asource voltage via a command sequence, wherein the phase control devicesrespectively issue a first command for energizing the first phase (Rphase) at any time, a second command for energizing the second phase (Sphase) at the predetermined electrical phase angle of a second-to-thirdphase (S-to-T phase) voltage in response to detection of a zero point ofa second-to-third phase (S-to-T phase) voltage by the second-to-thirdphase voltage measuring transformer after an energizing of the firstphase (R phase), and a third command for energizing the third phase (Tphase) at the predetermined electrical phase angle of a third-to-firstphase (T-to-R phase) voltage in response to detection of a zero point ofa third-to-first phase (T-to-R phase) voltage by the third-to-firstphase voltage measuring transformer at a time around ⅓ of a cycle afteran energizing time of the second phase (S phase).
 11. A synchronousswitching apparatus for use with a multiple phase power system having aplurality of phases and for detecting a source voltage of each phase andenergizing each phase at an electrical phase angle predetermined foreach phase, comprising: a plurality of switching devices, one switchingdevice being provided for each phase and opening and closing animpedance load; a plurality of switching mechanisms, closing and openingthe switching devices; a plurality of voltage measuring transformers,measuring source voltages of the phases; a plurality of phase-to-phasevoltage measuring transformers, measuring respective phase-to-phasevoltages; and a plurality of phase control devices, one phase controldevice being provided for each phase and issuing a command to energizethe impedance load with a source voltage at an electrical phase angle ina range predetermined for the phase, in response to detection of a zeropoint of a source voltage of the phase by the voltage measuringtransformer or to detection of a zero point of the phase-to-phasevoltage by the phase-to-phase voltage measuring transformer, wherein thesynchronous switching apparatus is adapted for use with an impedanceload in the form of capacitor banks with a neutral point grounded ortransmission lines without an electric charge, wherein: the plurality ofphases comprises a first phase (R phase), a second phase (S phase), anda third phase (T phase); the plurality of voltage measuring transformerscomprises a first, a second, and a third voltage measuring transformer,measuring source voltages of the first, second, and third phases,respectively; and the predetermined electrical phase angles of each ofthe first, second, and third phases are within a range of 0 degrees(zero voltage points of the R, S, and T phases) ±20 degrees, wherein,the impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first phase (R phase) at the predeterminedelectrical phase angle of the first phase (R phase) in response todetection of a zero point of a first phase (R phase) source voltage bythe first voltage measuring transformer, a second command for energizingthe third phase (T phase) at the predetermined electrical phase angle ofthe third phase (T phase) in response to detection of a zero point of athird phase (T phase) source voltage by the third voltage measuringtransformer at a time around ⅓ of a cycle after an energizing time ofthe first phase (R phase), and a third command for energizing the secondphase (S phase) at the predetermined electrical phase angle of thesecond phase (S phase) in response to detection of a zero point of asecond phase (S phase) source voltage by the second voltage measuringtransformer at a time around ⅓ of a cycle after an energizing time ofthe third phase (T phase).
 12. A synchronous switching apparatus for usewith a multiple phase_ power system having a plurality of phases and fordetecting a source voltage of each phase and energizing each phase at anelectrical phase angle predetermined for each phase, comprising: aplurality of switching devices, one switching device being provided foreach phase and opening and closing an impedance load; a plurality ofswitching mechanisms, closing and opening the switching devices; aplurality of voltage measuring transformers, measuring source voltagesof the phases; a plurality of phase-to-phase voltage measuringtransformers, measuring respective phase-to-phase voltages; and aplurality of phase control devices, one phase control device beingprovided for each phase and issuing a command to energize the impedanceload with a source voltage at an electrical phase angle in a rangepredetermined for the phase, in response to detection of a zero point ofa source voltage of the phase by the voltage measuring transformer or todetection of a zero point of the phase-to-phase voltage by thephase-to-phase voltage measuring transformer, wherein the synchronousswitching apparatus is adapted for use with an impedance load in theform of capacitor banks with a neutral point grounded or transmissionlines without an electrical charge, wherein: the plurality of phasescomprises a first phase (R phase), a second phase (S phase), and a thirdphase (T phase); the plurality of phase-to-phase voltage measuringtransformers comprises a first-to-second (R-to-S phase), asecond-to-third (S-to-T phase), and a third-to-first (T-to-R phase)phase voltage measuring transformer, measuring a first-to-second, asecond-to-third, and a third-to-first phase voltage, respectively; andthe predetermined electrical phase angles of each of the first-to-secondphase voltage, the second-to-third phase voltage, and the third-to-firstphase voltage are within a range of −30 degrees ±20 degrees, wherein,the impedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the first phase (R phase) at the predeterminedelectrical phase angle of a first-to-second phase (R-to-S phase) voltagein response to detection of a zero point of a first-to-second phase(R-to-S phase) voltage by the first-to-second phase voltage measuringtransformer, a second command for energizing the third phase (T phase)at the predetermined electrical phase angle of a third-to-first phase(T-to-R phase) voltage in response to detection of a zero point of athird-to-first phase (T-to-R phase) voltage by the third-to-first phasevoltage measuring transformer at a time around ⅓ of a cycle after anenergizing time of the first phase (R phase), and a third command forenergizing the second phase (S phase) at the predetermined electricalphase angle of a second-to-third phase (S-to-T phase) voltage inresponse to detection of a zero point of a second-to-third phase (S-to-Tphase) voltage by the second-to-third phase voltage measuringtransformer at a time around ⅓ of a cycle after an energizing time ofthe third phase (T phase).
 13. A synchronous switching apparatus for usewith a multiple phase power system having a plurality of phases and fordetecting a source voltage of each phase and energizing each phase at anelectrical phase angle predetermined for each phase, comprising: aplurality of switching devices, one switching device being provided foreach phase and opening and closing an impedance load; a plurality ofswitching mechanisms, closing and opening the switching devices; aplurality of voltage measuring transformers, measuring source voltagesof the phases; a plurality of phase-to-phase voltage measuringtransformers, measuring respective phase-to-phase voltages; and aplurality of phase control devices, one phase control device beingprovided for each phase and issuing a command to energize the impedanceload with a source voltage at an electrical phase angle in a rangepredetermined for the phase, in response to detection of a zero point ofa source voltage of the phase by the voltage measuring transformer or todetection of a zero point of the phase-to-phase voltage by thephase-to-phase voltage measuring transformer, wherein the synchronousswitching apparatus is adapted for use with an impedance load in theform of capacitor banks with a neutral point ungrounded, wherein: theplurality of phases comprises a first phase (R phase), a second phase (Sphase), and a third phase (T phase); the plurality of voltage measuringtransformers comprises a second and a third voltage measuringtransformer, measuring source voltages of the second and third phases,respectively; the predetermined electrical phase angle of the secondphase is within a range of 0 degrees ±20 degrees; and the predeterminedelectrical phase angle of the third phase is within a range of 30degrees±20 degrees; wherein, the impedance load is energized with asource voltage via a command sequence, wherein the phase control devicesrespectively issue a first command for energizing the first phase (Rphase) at any time, a second command for energizing the third phase (Tphase) at the predetermined electrical phase angle of the third phase (Tphase) in response to detection of a zero point of the third phase (Tphase) source voltage by the third voltage measuring transformer afteran energizing of the first phase (R phase), and a third command forenergizing the second phase (S phase) at the predetermined electricalphase angle of the second phase (S phase) in response to detection of azero point of a second phase (S phase) source voltage by the secondvoltage measuring transformer at a time around ¼ of a cycle after anenergizing time of the third phase (T phase).
 14. A synchronousswitching apparatus for use with a multiple phase power system having aplurality of phases and for detecting a source voltage of each phase andenergizing each phase at an electrical phase angle predetermined foreach phase, comprising: a plurality of switching devices, one switchingdevice being provided for each phase and opening and closing animpedance load; a plurality of switching mechanisms, closing and openingthe switching devices; a plurality of voltage measuring transformers,measuring source voltages of the phases; a plurality of phase-to-phasevoltage measuring transformers, measuring respective phase-to-phasevoltages; and a plurality of phase control devices, one phase controldevice being provided for each phase and issuing a command to energizethe impedance load with a source voltage at an electrical phase angle ina range predetermined for the phase, in response to detection of a zeropoint of a source voltage of the phase by the voltage measuringtransformer or to detection of a zero point of the phase-to-phasevoltage by the phase-to-phase voltage measuring transformer, wherein thesynchronous switching apparatus is adapted for use with an impedanceload in the form of capacitor banks with a neutral point ungrounded,wherein: the plurality of phases comprises a first phase (R phase), asecond phase (S phase), and a third phase (T phase); the plurality ofvoltage measuring transformers comprises a first and a third voltagemeasuring transformer, measuring source voltages of the first and thirdphases, respectively; the predetermined electrical phase angle of thefirst phase is within a range of 30 degrees±20 degrees; and thepredetermined electrical phase angle of the third phase is within arange of 0 degrees±20 degrees; wherein, the impedance load is energizedwith a source voltage via a command sequence, wherein the phase controldevices respectively issue a first command for energizing the secondphase (S phase) at any time, a second command for energizing the firstphase (R phase) at the predetermined electrical phase angle of the firstphase (R phase) in response to detection of a zero point of a firstphase (R phase) source voltage by the first voltage measuringtransformer after the energizing of the second phase (S phase), and athird command for energizing the third phase (T phase) at thepredetermined electrical phase angle of the third phase (T phase) inresponse to detection of a zero point of a third phase (T phase) sourcevoltage by the third voltage measuring transformer at a time around ¼ ofa cycle after a energizing time of the first phase (R phase).
 15. Asynchronous switching apparatus for use with a multiple phase powersystem having a plurality of phases and for detecting a source voltageof each phase and energizing each phase at an electrical phase anglepredetermined for each phase, comprising: a plurality of switchingdevices, one switching device being provided for each phase and openingand closing an impedance load; a plurality of switching mechanisms,closing and opening the switching devices; a plurality of voltagemeasuring transformers, measuring source voltages of the phases; aplurality of phase-to-phase voltage measuring transformers, measuringrespective phase-to-phase voltages; and a plurality of phase controldevices, one phase control device being provided for each phase andissuing a command to energize the impedance load with a source voltageat an electrical phase angle in a range predetermined for the phase, inresponse to detection of a zero point of a source voltage of the phaseby the voltage measuring transformer or to detection of a zero point ofthe phase-to-phase voltage by the phase-to-phase voltage measuringtransformer, wherein the synchronous switching apparatus is adapted foruse with an impedance load in the form of capacitor banks with a neutralpoint ungrounded, wherein: the plurality of phases comprises a firstphase (R phase), a second phase (S phase), and a third phase (T phase);the plurality of voltage measuring transformers comprises a first and asecond voltage measuring transformer, measuring source voltages of thefirst and second phases, respectively; the predetermined electricalphase angle of the first phase is within a range of 0 degrees±20degrees; and the predetermined electrical phase angle of the secondphase is within a range of 30 degrees ±20 degrees; wherein, theimpedance load is energized with a source voltage via a commandsequence, wherein the phase control devices respectively issue a firstcommand for energizing the third phase (T phase) at any time, a secondcommand for energizing the second phase (S phase) at the predeterminedelectrical phase angle of the second phase (S phase) in response todetection of a zero point of a second phase (S phase) source voltage bythe second voltage measuring transformer after the energizing of thethird phase (T phase), and a third command for energizing the firstphase (R phase) at the predetermined electrical phase angle of the firstphase (R phase) in response to detection of a zero point of a firstphase (R phase) source voltage by the first voltage measuringtransformer at a time around ¼ of a cycle after an energizing time ofthe second phase (S phase).
 16. A synchronous switching apparatus foruse with a multiple phase power system having a plurality of phases andfor detecting a source voltage of each phase and energizing each phaseat an electrical phase angle predetermined for each phase, comprising: aplurality of switching devices, one switching device being provided foreach phase and opening and closing an impedance load; a plurality ofswitching mechanisms, closing and opening the switching devices; aplurality of voltage measuring transformers, measuring source voltagesof the phases; a plurality of phase-to-phase voltage measuringtransformers, measuring respective phase-to-phase voltages; and aplurality of phase control devices, one phase control device beingprovided for each phase and issuing a command to energize the impedanceload with a source voltage at an electrical phase angle in a rangepredetermined for the phase, in response to detection of a zero point ofa source voltage of the phase by the voltage measuring transformer or todetection of a zero point of the phase-to-phase voltage by thephase-to-phase voltage measuring transformer, wherein the synchronousswitching apparatus is adapted for use with an impedance load in theform of capacitor banks with a neutral point ungrounded, wherein: theplurality of phases comprises a first phase (R phase), a second phase (Sphase), and a third phase (T phase); the plurality of phase-to-phasevoltage measuring transformers comprises a second-to-third (S-to-Tphase) and a third-to-first (T-to-R phase) phase voltage measuringtransformer, measuring a second-to-third and a third-to-first phasevoltage, respectively; the predetermined electrical phase angle of thesecond-to-third phase voltage is within a range of −30 degrees ±20degrees; and the predetermined electrical phase angle of thethird-to-first phase voltage is within a range of 0 degrees ±20 degrees,wherein, the impedance load is energized with a source voltage via acommand sequence, wherein the phase control devices respectively issue afirst command for energizing the first phase (R phase) at any time, asecond command for energizing the third phase (T phase) at thepredetermined electrical phase angle of a third-to-first phase (T-to-Rphase) voltage in response to detection of a zero point of athird-to-first phase (T-to-R phase) voltage by the third-to-first phasevoltage measuring transformer after the energizing of a first phase (Rphase), and a third command for energizing the second phase (S phase) atthe predetermined electrical phase angle of a second-to-third phase(S-to-T phase) voltage in response to detection of a zero point of asecond-to-third phase (S-to-T phase) voltage by the second-to-thirdphase voltage measuring transformer at a time around ¼ of a cycle afteran energizing time of the third phase (T phase).
 17. A synchronousswitching apparatus for use with a multiple phase power system having aplurality of phases and for detecting a source voltage of each phase andenergizing each phase at an electrical phase angle predetermined foreach phase, comprising: a plurality of switching devices, one switchingdevice being provided for each phase and opening and closing animpedance load; a plurality of switching mechanisms, closing and openingthe switching devices; a plurality of voltage measuring transformers,measuring source voltages of the phases; a plurality of phase-to-phasevoltage measuring transformers, measuring respective phase-to-phasevoltages; and a plurality of phase control devices, one phase controldevice being provided for each phase and issuing a command to energizethe impedance load with a source voltage at an electrical phase angle ina range predetermined for the phase, in response to detection of a zeropoint of a source voltage of the phase by the voltage measuringtransformer or to detection of a zero point of the phase-to-phasevoltage by the phase-to-phase voltage measuring transformer, wherein thesynchronous switching apparatus is adapted for use with an impedanceload in the form of capacitor banks with a neutral point ungrounded,wherein: the plurality of phases comprises a first phase (R phase), asecond phase (S phase), and a third phase (T phase); the plurality ofphase-to-phase voltage measuring transformers comprises afirst-to-second (R-to-S phase) and a third-to-first (T-to-R phase) phasevoltage measuring transformer, measuring a first-to-second and athird-to-first phase voltage, respectively; the predetermined electricalphase angle of the first-to-second phase voltage is within a range of 0degrees ±20 degrees; and the predetermined electrical phase angle of thethird-to-first phase voltage is within a range of ±30 degrees ±20degrees, wherein, the impedance load is energized with a source voltagevia a command sequence, wherein the phase control devices respectivelyissue a first command for energizing the second phase (S phase) at anytime, a second command for energizing the first phase (R phase) at thepredetermined electrical phase angle of a first-to-second phase (R-to-Sphase) voltage in response to detection of a zero point of afirst-to-second phase (R-to-S phase) voltage by the first-to-secondphase voltage measuring transformer after the energizing of the secondphase (S phase), and a third command for energizing the third phase (Tphase) at the predetermined electrical phase angle of the third-to-firstphase (T-to-R phase) voltage in response to detection of a zero point ofa third-to-first phase (T-to-R phase) voltage by the third-to-firstphase voltage measuring transformer at a time around ¼ of a cycle aftera energizing time of the first phase (R phase).
 18. A synchronousswitching apparatus for use with a multiple phase power system having aplurality of phases and for detecting a source voltage of each phase andenergizing each phase at an electrical phase angle predetermined foreach phase, comprising: a plurality of switching devices, one switchingdevice being provided for each phase and opening and closing animpedance load; a plurality of switching mechanisms, closing and openingthe switching devices; a plurality of voltage measuring transformers,measuring source voltages of the phases; a plurality of phase-to-phasevoltage measuring transformers, measuring respective phase-to-phasevoltages; and a plurality of phase control devices, one phase controldevice being provided for each phase and issuing a command to energizethe impedance load with a source voltage at an electrical phase angle ina range predetermined for the phase, in response to detection of a zeropoint of a source voltage of the phase by the voltage measuringtransformer or to detection of a zero point of the phase-to-phasevoltage by the phase-to-phase voltage measuring transformer, wherein thesynchronous switching apparatus is adapted for use with an impedanceload in the form of capacitor banks with a neutral point ungrounded,wherein: the plurality of phases comprises a first phase (R phase), asecond phase (S phase), and a third phase (T phase); the plurality ofphase-to-phase voltage measuring transformers comprises afirst-to-second (R-to-S phase) and a second-to-third (S-to-T phase)phase voltage measuring transformer, measuring a first-to-second and asecond-to-third phase voltage, respectively; the predeterminedelectrical phase angle of the first-to-second phase voltage is within arange of −30 degrees ±20 degrees; and the predetermined electrical phaseangle of the second-to-third phase voltage is within a range of 0degrees ±20 degrees, wherein, the impedance load is energized with asource voltage via a command sequence, wherein the phase control devicesrespectively issue a first command for energizing the third phase (Tphase), a second command for energizing the second phase (S phase) atthe predetermined electrical phase angle of a second-to-third phase(S-to-T phase) voltage in response to detection of a zero point of asecond-to-third phase (S-to-T phase) voltage by the second-to-thirdphase voltage measuring transformer after the energizing of the thirdphase (T phase), and a third command for energizing the first phase (Rphase) at the predetermined electrical phase angle of a first-to-secondphase (R-to-S phase) voltage in response to detection of a zero point ofa first-to-second phase (R-to-S phase) voltage by the first-to-secondphase voltage measuring transformer at a time around ¼ of a cycle afteran energizing time of the second phase (S phase).
 19. A synchronousswitching apparatus for use with a multiple phase power system having aplurality of phases and for detecting a source voltage of each phase andenergizing each phase at an electrical phase angle predetermined foreach phase, comprising: a plurality of switching devices, one switchingdevice being provided for each phase and opening and closing animpedance load; a plurality of switching mechanisms, closing and openingthe switching devices; a plurality of voltage measuring transformers,measuring source voltages of the phases; a plurality of phase-to-phasevoltage measuring transformers, measuring respective phase-to-phasevoltages; a plurality of phase control devices, one phase control devicebeing provided for each phase and issuing a command to energize theimpedance load with a source voltage at an electrical phase angle in arange predetermined for the phase, in response to detection of a zeropoint of a source voltage of the phase by the voltage measuringtransformer or to detection of a zero point of the phase-to-phasevoltage by the phase-to-phase voltage measuring transformer; surgeabsorbers provided between respective phases and ground for respectivelysuppressing surge voltages of respective phases; and surge absorbersprovided between respective phases for suppressing phase-to-phase surgevoltages.